How do I fix a broken cable that won’t let the screen turn on?

my nephew dropped his nintendo switch lite, not hard, but the screen on the left side popped out but the switch still worked perfectly fine. i took it somewhere to get fixed and he said that a cable came out of place and that’s what was stopping the screen from popping back in, said it was an easy fix and all he had to do was push it back in place. then he called and said he “underestimated” the cable and busted it and the screen won’t turn on but he would fix what he broke for $150? so anyways, the switch technically does still turn on. like it makes all the sounds and i can scroll and click on a game and the music will start playing for it but you can’t actually see anything on the screen. i already bought him a new regular nintendo switch so i’m just trying to fix this by myself but i have no idea what’s wrong or what to do. any tips?