The Set-DnsServerForwarder cmdlet changes forwarder settings on a Domain Name System (DNS) server. This cmdlet sets or resets IP addresses to which the DNS server forwards DNS queries when it cannot resolve them locally. This cmdlet overwrites existing server level forwarders.
or using the GUI
Open the DNS server properties dialog box by right clicking on the server and choosing properties.
Click to the forwarders tab and to add another forwarder click edit.
Click in the top line and put in the ip address of the DNS server you want to use as an example.
I used 184.108.40.206 which is one of googles servers if it resolves click ok and you have set up a forwarder.