Long ago, you could setup a Linux box and edit the /etc/resolv.conf file knowing the changes would stick. That made it incredibly simple to manage what DNS servers would be used by the machine. Fast-forward to now, and a manual edit of that same file will only be overwritten anytime you restart networking or reboot the machine.
Fortunately, this is Linux, so taking back control of the resolv.conf file isn’t much of a challenge… when you know what to look for. Let me serve as your guide in this quest. With a little work at the command line, you’ll be able to dictate exactly what goes into that resolv.conf file without issue.