You are right, Unison customers do have to use the user portal or the Rogers Unison mobile app to access their forwarding options. Have you tried the Rogers Unison mobile app? You may find that convenient in comparison to the portal.
If you require technical assistance with the feature you can reach out to our Rogers Unison Technical Support Consultants at 1-866-727-2141. For Live Chat or to use the Get a Call Back feature please visit the Rogers Unison page.