Admin URL not working

Alright, so I’m used to godaddy to install wordpress, I setup my site and now I want it to have a custom domain, I go into wordpress dashboard, then general settings and change the site address to my domain name which is d2apdesigns.com from there I copy my wordpress files to the FTP file manager root, and everything fine is fine, I have a custom domain and what not but I lost admin rights, so I un-did everything and got the admin rights back, but what can I do to keep my custom domain and admin rights? How come the admin URL doesn’t work?