It does not sound that you have a static IP address. A static address is entered into the client, in your case the router. In the router WAN area the configuration should look something like this:
View attachment 43782
The WAN IP Setting should have entries for a public IP address with all three settings entered.
If your ISP is giving you a reserved IP address that your router is getting via DHCP the Basic Config will look like this:
View attachment 43783
In either case you can manually select the DNS servers for your router. The WAN DNS Settings looks like:
View attachment 43784
You can choose the desired DNS server by clicking on the Assign button. In my example I have manually entered Cloudflare Secure servers with an IP address of 1.1.1.2 and 1.0.0.2. What yo use is your choice but I recommend a service that filters malware at a minimum.
As for InstantGuard not working you need to have a Public IP address, a working DDNS entry or a valid static IP address. To determine if you have a public IP address see:
https://www.meridianoutpost.com/resources/articles/IP-classes.php