Changed WP/Site URL, but still accessing from old URL

You can add the following redirect rule in .htaccess file of https://gpmasonry.elmcreates.com/ to redirect the domain to https://gp-masonry.com/

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} !gpmasonry.elmcreates.com$ [NC]
RewriteRule ^(.*)$ https://gp-masonry.com/$1 [L,R=301]

Thanks for the suggestion. But my client’s IT person won’t transfer the domain to me and he won’t let me host the website with his hosting provider.

He is pointing https://gp-masonry.com at https://gpmasonry.elmcreates.com.

Whenever I redirect https://gpmasonry.elmcreates.com to https://gp-masonry.com the website gets stuck in an infinite redirect loop and won’t load.