Hey bro, I would try to take it back apart and check your connection of the display to the main board. the screen has to be backlit and that is what allows you to see whats on it. if you can see the screen faintly then it’s getting the display information but with out being backlit you wont be able to read it. Most screens have a separate power inverter to handle backlighting. Update (05/05/2021): If you can check it against a known good screen, You might have gotten unlucky and just gotten a bad screen. good luck. I would call and get a new one if you dont have luck soon.
I’m reading the entire watch can be sold for as little as ten dollars, I would buy a new one, and then use your broken one for parts as you need them. Good luck my friend! There are many services that offer mail in but I dont its worth sending it in.