In Pipedrive, navigate to Settings > Company overview > Manage users. From the user's meatball menu on the far-right (...) select User overview.
The user ID is the number at the end of the page URL, e.g. https://shiptheory.pipedrive.com/users/details/12345678
In RingCentral, navigate to Users and select the user's name.
The extension ID is the number towards the end of the page URL, e.g. https://service.ringcentral.co.uk/application/users/users/default/1234567890/settings/default