Acquire the LCD screen, make sure it works.

Open the enclosure carefully.

Unscrew the screen, make sure all connector stay connected (or the rubber conductors), they are hard to connect back.

Depending on the screen, some have reflecting/blocking layers behind the screen, remove it CAREFULLY and make sure you don't remove the polarizing filters (Should have one on both sides)

Make sure light can pass through the screen (means you can see through). Make sure both polarizing filters are intact, do NOT remove them.

Mount the screen so that it does not move and you can display images on it.

Set up the light source and make it so that entire screen is lit brightly.

Set up the lense, the bigger your screen is the bigger lense you need.

Turn on the light and focus the image, if it is low contrast, tilt the screen a bit. It might need some fiddling to get it right. A good glass (strong) magnifying glass is a big plus here.

Write the code and start playing snake on your wall, if you are creative, you can even create a motion tracking system and can make the screen touch sensitive.

Make a nice enclosure for the projector, to just display the picture, not to light up the room. (But make sure nothing catches fire or heats up too much!)