We have changed DNS server IP address so where would I find that on the DNS setting on UC server? I prefer to do it through the GUI.
You need to change them via CLI, not GUI.
You can refer to the CLI administration guide for the commands to view/change the DNS.
If you would have used the search functionality in the community or simply searched on the topic in a search engine you would likely have found amongst others this post.
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: