I retired my DI-LB604 about 5 years ago, so I could not connect to it to get a screen shot, but I think that the screen shot below taken from the on-line emulator at »support.dlink.com/emulat ··· zard.htm
will show you where to find the Virtual Server setup page to do what you want to do.
If you are looking for a specific menu selection for Citrix, you won't find it, but you can create your own Citrix Virtual Server entry and manually enter the proper ports to be forwarded yourself.
A well-regulated militia, being necessary to the security of a free State, the right of the people to keep and bear arms shall not be infringed.
When governments fear people, there is liberty. When the people fear the government, there is tyranny.