Sophos 17 XG port forwarding

Question

Hi 
 I'm new on Sophos product and I have a problem with port forwarding. 
 I have couple servers (and other devices with same problem) I need to have access to, for the first one I have no problem I do the 3389 to 3389 but when i want to do it for the 2nd like to forward 3389 to 3390 or any other port I don't know how to do that. When I check the "Change Destination Port(s)" only the "to" area is disabled i can't write anything there. 
 
 If you can please show me how to do that. 
 Best regards

Youssef DEKRAOUI · Accepted Answer

Hi 
 I figured out the solution by myself :D 
 
 The problem I was having is that i don't have this forward type to port but i have service instead the thing the confused me. but I end up creating service with the rang port i wanted and it worked out.