How to Find a Custom Page Privilege and add to a Custom role assigned to specific users

Summary:

We have created a Custom Application Page with Sandbox (Application Composer).
User is able to access this custom page only when standard role Custom Objects Administration (ORA_CRM_EXTN_ROLE) is assigned to the user.

Is there a way to assign only this custom page access with a new custom role as we cannot assign a standard role to business users due to certain user activities that they cannot perform or assigned with.

How can I assign only this page access to a user? Can we create a custom role with only this privilege. How to find this custom page privilege to add to an role or create a new role.