Set up DNS Servers VPN

So trying to connect my VPN (TunnelBear) to my ancient laptop since my other laptop, the dc power jack is broken and going to send a complaint to the seller on ebay which i bought the replacement power part from which it never came. So back to the point so I followed their guide but I am stumped on the last part of how to set up DNS. Someone help me.

Set it to google (, or opendns (, or whichever other DNS server you'd like to use.