Enable Remote Desktop through IP Office Firewall

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I have literally one customer using the IP office as a router and now they want to have a few computers be accessible through the firewall via remote desktop client.

Lets say the public address is 233.243.123.95 (not the read address I know) with a mask of 255.255.255.248
Local address is 192.168.42.5
Mask 255.255.255.0
Port number is TCP 3389

Thanks in advance