Is it possible to copy games file to steam library to reduce data usage in downloading the game

Hello, I’m trying to copy the game files I bought from the game pass to steam library after I bought it too in summer sale (So I don’t download the file twice and to avoid too much data usage). The problem is it can’t connect to the steam account, making it impossible to multiplayer. Any helps or suggestions? Or should I redownload it again for the steam account?