If you've forgotten your password in Gems of War or need help recovering your account you'll need to contact support by submitting a request for help here.
Next time, ensure your password is noted down. If you want to link your account to another platform or recover a game account that you lost, you will need to verify your account and remember your password. Please note that console accounts are unable to link their game to other platforms, go here for more information.
Tip: For more information account linking see this article here: Save your progress: Account linking in Gems of War.