Sign on to your router, go to advance settings, then to the forwarding section, then to Virtual Servers then add you ports. Your User Interface may be a bit different but you are looking for the Virtual Servers window.

One other point, You should find the address reservation window and reserve an internal IP address such a 192.168.0.125 (one that is not being used) and assign it to the ported device's MAC address. Power cycle the router which should show that device assigned to that IP address. Now set up your port assignment using that IP address linked to that ports used by that device. May need to power cycle the router again.

@ArcherC8 I have located the Virtual Servers section. 

 

The problem remains that the fields AT&T asks you to fill out are not consistent with the fields in the Virtual Server. See below - I'm at a loss for how to fill out these fields.

 

You also mention assigning an IP to the "ported device" MAC address. I have seven different devices (mobile, computers) that all can use WiFi Calling. Are you saying I have to create reservations for each of these seven devices in order for any of them to use WiFi Calling?

 

The fields:

 

1. Service Type - ?
2. External Port ?
3. Internal IP - ?
4. Internal Port - ?
5. Protocol - UDP (the only one that AT&T's instructions offers up)

 

 

see https://community.tp-link.com/us/home/forum/topic/161612 for another vendor's WIFI which would be about the same. And this should help with the post numbers and types https://www.att.com/support/smallbusiness/article/smb-wireless/KM1305083/