Hi There,
We are really sorry to say that, we are not able to help you in this issue. This is because, we are not an expert in OAuth configuration.
We are only available to help you about our style’s features that we customized and added in our style.
In this issue, you need to hire someone else to help you, who is an expert in OAuth configuration for phpBB.
You could also review the below URLs, that will helpful to you.
https://www.phpbb.com/support/docs/en/3.1/ug/adminguide/general_client
https://wiki.phpbb.com/OAuth_Providers
Best Regards,
ThemeLooks Support Team