redirecting url using A-record

I had set up a new wordpress website on a domain reference, and when it came for the site to go live the client wanted to keep control of their domain and instead change the A-record of the domain to point at the domain reference where the website is.

This has worked fine for the homepage, but all the menu items of course still point to the domain reference pages. I have tried changing the site url and home in the General Settings, and have read lots of solutions that don’t quite match this situation, and nothing has had the right result

I want the site t be working properly, but without affecting the seo of the site if possible,

thanks.