DNS server wont change

so the thing is I tried to change my DNS server by going to

sudo nano /etc/dhcp/dhclient.conf

and changed

prepend Domain-name-servers 1.1.1.2,1.0.0.2,9.9.9.9;

and saved the file and did

sudo service NetworkManager restart

(since the sudo service network-manager restart doesn't work saying Unit network-manager.service not found.) and when I checked it using

cat /etc/resolv.conf

It only shows the default one which was already there so nothing is changed.

please help!

Couldn't find any solution so also sorry for my bad grammar if there's any mistake on it also I don't even know if I am writing this correctly or not since this is my first time writing.

Thank you for the help in advance.