If, during the first sign-in, you created an account via Google/Apple/Facebook login, you can link an email as a login through the option "Link email", located in your account's section in the game:
Please note that you can only link an email if it is not yet in use by another Gaijin account. Otherwise you can link a Gaijin account, if it wasn't previously used in War Thunder Mobile.
After linking an email login you will receive an email notification with the suggestion to change the password. After changing the password, you can access the account from either platform, using email login and password.