There is not a set of instructions specific for the LT1, but I will point you toward a helpful thread. First a few comments.
There exists a device I believe you can purchase that will interface with the programming pads visible at about 3 o’clock in the picture below. not a great pic, but I think you’ll get the idea. Lexel sells them. I’ve bought a D4 aux light board from him, he sent it quickly, and his prices are reasonable. I just haven’t ever motivated to get one of the programming keys, maybe some day. First the programming key pic, then the driver board with the pads at 3 o’clock.
I’m noticing more pins on the key than pads on the board, guessing you can/would figure that out, or Lexel could tell you.
In the event you don’t want to go that route, you will need an 8 pin chip clip to interface to the Attiny85 chip. This thread has lots of info to get you going. I used it when I began to learn to flash my D4. The only SW you need to load is the AVR Tools and the USBasp driver, unless you want to write/modify firmware, then I think ATMEL studio is useful (I’m guessing here).
Hope this helps, ask more questions as desired. 
Here’s the command if you want to flash the 27b version firmware Toykeeper posted above:
avrdude -c usbasp -p t85 -u -Uflash:w:anduril.2019-11-27b.blf-lantern.hex