I dedome while still hot after reflowing, (or after running the light briefly). I use tweezers to push, lift, and peel the dome off. It tends to come off in one piece when not cold. I also use a plastic toothpic to remove any dome bits that remain attached to the LED die.
this is how Artiet59 does it… imo his QTip technique works very well
there is also a post about slicing (I dont slice)