Tiny URL points to the wrong website

I am pretty sure this is a really simple problem, but I am having trouble figuring it out.

A few months ago I developed a wordpress site for a friend on my server. I then transfered the site to his server and everything seems to be working just fine.

However, if makes a tiny URL with the button at the top of a post that tiny URL links back to my website.

The Tiny URL looks correct https://www.hisdomain.com , but if you click on the link it sends you to my homepage.

My assumption is that there is some place in the admin section of his site where I forgot to change the URL from my website to his new domain name when I moved the site from the test environment on my server to his server, but I am not sure where to go in the admin panel to find fix it, or maybe it is a totally different issue. Any help you can provide a rookie trying to help a friend would be appreciated.