BUT I WANT TO CHANGE MY SERVER IP

what is your DNS name? do you own one?
if you don't have a domain name you can't do it.
You need to log into your control panel where you manage your DNS records like in go-daddy or cloudflare or wherever you have your domain name parked and you have to assign a subdomain of type A which points to the new IP address. then you go into the page that burn linked in the previous page and put that subdomain in.

HOW TO KNOW THAT WHAT IS YOUR DOMAIN NAME

AND SUBDOMAIN

AND I AM ADMIN OF MY COMPUTER

I WANT TO CHANGE IP ADRESS OF MY SERVER IN GAMETRACKER CS1.6

WHEN I ENTER SUBDOMAIN IN DNS TAB

DNS name does not resolve to a valid IP address

GameTracker does not allow manual IP changes for servers. If your server’s IP changes (e.g., due to dynamic IP), you’ll need to re-add it as a new server with the updated IP. There’s no way to update the IP of an existing listing.