Everything is tied to your GWENT account; there are no save files. All you need to do with the new PC is to install Galaxy and the game, and you'll be good to go.
You can find the TB savegames in one of the two folders below:
"C:\Users\<Your username>\AppData\Local\Temp\CDProjektRED"
"C:\Users\<Your username>\AppData\LocalLow\CDProjektRED"
You can find the TB savegames in one of the two folders below:
"C:\Users\<Your username>\AppData\Local\Temp\CDProjektRED"
"C:\Users\<Your username>\AppData\LocalLow\CDProjektRED"