Solution Workaround - Forward port to missing device
If you need to forward a port to device not on the device list.
1. Disconnect the device you want to forward to from network
2. Set another device to the IP you want in DHCP reservations and reboot it (use a high number, youll see why in step 4, I used 250)
3. Forward the port to the device
4. Disconnect the temporary device from network
5. Change the DHCP pool to EXCLUDE the number you just used (I set 10-249)
6. Reconnect device you want the port forwarded to and set it a static IP of the address you jsut used I used 192.168.68.250
This onld works if you can set a static IP on the target device, e.g. a windows or linux machine.