Response port masking

Our F5 is forwarding traffic to IIS web servers on non-standard ports (such as 8081). The application on the web server will send traffic back to http://app.blah.com:8081.

How do I get the F5 to remove the port number from the response that is sent back to the client - in other words replace any instance of http://app.blah.com:8081 with http://app.blah.com in the response?

This is a similar question to https://community.f5.com/t5/technical-forum/remove-port-from-http-response/td-p/109510 however it is not detailed as to what was done, i woould highly appreciate your feedback