Yea, I struggled with a second build of my new GS. It was because the screen had the ribbon backwards/upside down. I remembered it being simple, and it is.
You just follow these steps:
1- Destatic yourself. Touch some metal.
2- Only touch the edges of the boards.
3- On the screen module, pull out those 2 plastic gray tabs and it will release the ribbon. Flip it over if installed from the factory upside down. Hold ribbon still, press tabs in. Screen done.
4- The other end, the teeth of the ribbon goes into the slot very easily into the motherboard with chips and connectors exposed facing up. If you struggle, be very careful since this can mess up some pins (it’ll take a lot of pressure to really mess it up though).
Both modules should align so you can sandwich them perfectly one on top of the other as a stack