There are 2 main ways to solve this issue.
1. You are responsible for the project and you are taking care of the configs. In this case you really need to know what Kamailio and it config is. Here I'd start with
https://www.asipto.com/sw/kamailio-admin-book/ as a basic for a SIP protocol and later - how it's processed in Kamailio perspective. havfo's kamailio config is quite advanced i
2. Find someone who will do it on a payment basis.
P.S: Have you tried to specify in your SIP client everything, as you are connecting to your VoIP provider, but adding
WEBRTC-to-SIP server as outbound proxy?