Due to legal and platform restrictions, you can't play the same game between console/Switch and other platforms.
If you can't see your password or an "Account" option in Settings, this is because Gems of War does not support account linking between your console and other devices. However, your account progress on Xbox, PS4, and Switch is tied to your Xbox Live, PSN or Nintendo Online accounts respectively, so you can still reinstall the game when logged into these without a loss of progress.
What can I do instead?
You can play the same Gems of War game account on mobile and PC. However, you'll have to start a new game if you are playing on console and want to play on Steam or mobile as well.
TIP: Playing on Steam/mobile? Check out this article to link your account between devices.