Can you access PlayerGui from server script? If yes, how?
I always get this: ScreenGui is not a valid member of PlayerGui
Quick answer: No, you cannot access the PlayerGui from a server script.
But don't lose hope, you can use the server script to ask a local script to do what you want.
You can do this using RemoteEvents and RemoteFunctions. (https://developer.roblox.com/en-us/articles/Remote-Functions-and-Events)
The idea is that the server script triggers a remoteEvent that the local script is listening for. Once the local script sees that the remoteEvent has been triggered, the local script performs an action with arguments passed through the remoteEvent.
I can't provide any further help without knowing specifics. If you want more info on how to use these, feel free to message me. Good luck with your game.