As long as you use the same email address to log in via social providers you can link your Google or Apple account to your ATG Tickets account.
Simply select either "Sign in with Google" or "Sign in with Apple" and enter your email address. You will receive the below pop up and will be prompted to enter in your existing password for your ATG Tickets account - If you have forgotten your password for this account, please select the "Forgotten your password?" link to verify your account and reset the password.
Please note - using "hide my email" when signing in by Apple will create a new account and will not link existing ATG Tickets accounts with Apple.