So I put a new LED into my P-Rocket, a NW T6 XML, however I somehow knocked the LED off of the star when twisting the bezel back on. Everything seems ok other than that still so I should be able to reflow it on again, but how? Never done this before so advice/help needed.
Wait until your wife leaves the house this is key. Take a frying pan and put it on the stove set to 350F. Place the emitter board on the pan drop the emitter on in the perfect location. Watch closely until the solder starts to bubble than turn the stove off and let it cool. You have now reflowed your first emitter congratulations.
What E1320 said. Just don't forget to add a thin layer of flux to the pads. Aligning the emitter perfectly pre-flow can be kind of tricky. But as long as you have a little bit of flux on there, once the pads heat up, the emitter will kind of suck itself on to the star's pads and align itself perfectly. Doing it without flux is a lot harder and also increases your chances of getting a weak bond which may result in you breaking the emitter off the board again.
Our stove doesn't have temp settings, just Lo-Med-Med/Hi-Hi, lol. I honestly have no clue what setting will be what temp, guess I can just ramp up until it works.
Hmmm.
Try Med at first then if it takes too long go Med/High. Then again it might not be good to even try Med setting, might just go to your Med/High setting and mind it well.
I once used the oven to to remove headlight lenses from the housing to modify with some LED bulbs and in the middle of the baking ramped up the heat and monitored it constantly to make sure I did not over bake the other components involved.
It depends on the range and the pan, but I would start on low and work my way up. It doesn't take that much heat to get the solder to flow.
As you raise the temp, keep an eye on the emitter. You'll know you succeeded when you see the emitter sort of pop into place onto the pads like at the 40 sec mark of this video.
For reference, I use a gas range and an old ano aluminum pan. I use the smallest burner, used for simmering, at about quarter burn and the pan gets up to temp in a few minutes.
The other option is to actually bake it in the oven. If you're oven will go to 500F (260C), I would go that route. It's far gentler on the LED since the assembly will heat up slower. Heat-Shocking an LED is really not good for it.
For flux, either use No-Clean, or, use water-soluble. if you use water-soluble, you'll have to wash the whole thing in the sink under HOT water really well after reflow.
Warm the oven up to 500F, put the star board in on a cookie sheet, wait for the solder to go molten (it will get very shiny), and then turn off the oven and open the oven door. Once the solder sets back up, pull the cookie sheet out and let it cool down to room temp.
PPtk
If only you knew the heat shocks they undergo in making them 
If only you knew that they are manufactured in a zero-humidity environment where moisture sensitivity isn't a problem. Most people here doing reflow at home are not going to be working with properly desiccated emitters and could easily damage an LED by heat-shocking them.
PPtk
I manufacture them, I work for Cree, I am a process engineer there.
Cool job :)
Long quote is long.^^
I once bought some warm white Cree's from DX and some loose stars. I soldered them on small steel plate (as I did not have a disposable pan) on the gas stove, on a very low flame. That was using solder paste from DX. Do not handle the solder paste in the kitchen. Just after the flux bubbled and the solder melted, I put the bottom of the steel plate in cold water to prevent overheating everything. With a small pan, that would have been easier, as there would be less rish getting the hot star or emitter wet.
- I would not put that puppy in the over. Reflow soldering is not done in any heated enclosue, oven or otherwise.
- Just put the star on a piece of aluminium or copper and support it where u have access to the bottom,
- Use a small propane or butane torch and heat the bottom of the metal until the solder flows then remove the heat.
Say WHAT? We call it a "Reflow Oven". Please keep your torch away from my electronics.
http://speedlinetech.com/electrovert/omnies.aspx
As an example.. Reflow Solder's very nicely, and makes Tollhouse cookies really well.
I mean seriously? A controlled environment with a slow and gradual heat rise (oven) or the merciless and completely uncontrolled heating from a torch flame? Really?
PPtk
I was caught by my wife in the act of reflowing some components, using a frying pan on the stove in the kitchen. Honestly, in twelve years of marriage I have never seen her as angry as she was that night!
Few days ago I removed XPG from PCB and replaced it with Nichia 219 using 40W soldering iron... Weller, if that's of any importance...
Held the PCB with needle-nose pliers (with piece of rubber as thermal insulation), told my friend to grab LED and EASILY pull it off PCB... once off, used a TINY bit off flux on all three spots and aligned Nichia LED as best as I could... placed PCB over thick part of soldering iron and few seconds later - floooow... LED aligned itself and now I'm EDCing beautiful little lamp with beautiful tint... :-)
Indeed, normally reflow soldering is done in an oven.
But with the LED mounted on a thermally conductive board, heating from below is the safest way. Heating from above in an uncontrolled way might overheat the LED while the board is taking a longer time to warm up.
Do not heat the board directly with a flame, but put something in between. There will be a thin layer of air that slows the heating. If the heat is not too high, solder temp will be reached in half a minute or a minute, so it is easy anough to take the pan off the heat and into some water.
That isn't reflow soldering, cheaplite. That's called Wave soldering. The board literally passes over a flowing 'wave' or fountain of molten solder. Completely different process and almost exclusively used for through-hole components. Surface mount is equally almost exclusively soldered in a reflow oven.
PPtk