I need to reset my DNS server

I used VPN to watch Netflix, but after I turned it off I got Netflix Error M7111-5059 (https://help.netflix.com/en/node/53047).

I restarted the WiFi router many times but the issue still persists. I contacted Netflix and they had me go to https://fast.com/# to locate my service. Both Client and Servers are in the US, no other countries listed.

They said that I had to contact Xfinity to reset/switch my DNS server back somehow.