This guide describes how to change domain for a website in the Templ Panel.
NOTE: You need to add the domain in the control panel first!
Step 1: Click on Websites in the left menu, then click on the website that you want to change domain for.
Step 2: Click on Edit Website Details.

Step 3: Under "Domain", choose your domain in the list.

Step 4: Scroll all the way down and click Continue, that's it!
Related: How to update your name servers.