How to configure authorization URL for SSO in OAuth 2.0

Hello.

I created a mobile app. 
I have a requirement to reduce the time to log for SSO.
Currently, for SSO, users have to click "Use Single Sign On(SSO)" on the login page and enter an email address.
The new requirement is skipping those steps. 

Could I show the specific login page first for SSO?
How to configure the authorization URL for SSO in OAuth 2.0?

Is there any way to reduce login steps for SSO?

Thanks