Port Mapping for Wireguard Server on AR750s

I am trying to map ports on the main router (AR750s is behind this router) so that I can run wireguard server on AR750s. Below is the screenshot. Now in configuration, I can see that there are two ports. How to configure port forwarding, any suggestions?

I think the settings are correct.

You can choose Protocol to UDP only

not familiar with your router but youmight choose user defined instead of application under type. and as long as you changed the default port on the glirouter in the wireguard server section from 51820 to 51915