When creating an IPsec location for the Web Security Service, FQDN were not supported until February 2018, and you could not configure a firewall/router device to use an FQDN instead of an IP address. As of March 2018, FQDN are an available option when using Firewalls and Routers that support this feature.
The rest of the procedure may be found here under your router's specification: VPN IKEv2 with Pre-Shared Key and Dynamic IP/FQDN