A Firewall rule allowing the port used by RDP (TCP/3389) from the zone containing your client machines (LAN/internal?) to the DMZ zone will allow these client machines to RDP to these servers.
As there are two versions of the Firewall currently in support (v7 - 7.0.1.03 and v8) which are slightly different - v7 uses "services" v8 uses "application", but the principle is the same for each.
There isn't a default serivce definition for RDP in v7 so you will need to create this entry manually. I do believe there is an "RDP" application definition present in v8, but if not the same applies. Once the service/application has been defined you will then be able to create the firewall access rule.
i got it ,thank you for help