unable to log in to dashboard on one site

My ex built some sites for me using WordPress templates (and a few html that I need to change to wp templates). Unfortunately, out of 41 sites there is one I can’t log into. I’ve tried every user id and password combo he ever used but still no luck. He let me transfer the domains at go daddy to my account that were under his name and I even set up my own account with the server he used to host my own accounts. All the files have been transferred over, but I can’t request new sign in info from wordpress because it’s listed under his email address. Help! Is there anything I can do short of redoing the whole site?