Please make sure you are configuring different sso for agents and contacts and if you don't see "are you a customer" button then please feel free to reach out to Freshdesk support.

Also, Ensure that you refer to the steps suggested for different IDP and sos type here- https://support.freshworks.com/support/solutions/articles/50000002351-what-is-and-how-to-configure-agent-sso-and-contact-sso-for-an-organization-

TIA :)