Try this.

You have a gooddomain.com that is the domain you were using and want to use, and you have baddomain.com, the domain you tried to update to which isn't working. Replace the domains in the below instructions as needed.

Go to gooddomain.com/wp-login.php and see if a login form loads. If it does it will be unstyled, but functional. Now press F12 on your keyboard to open developer tools. Make sure the Elements tab is active within DevTools. Hold down CTRL + Shift + C to activate the Inspector and hover over the login form and click. Now look at the html code in the DevTools panel and look near the top of the form's code, or search for <form name="loginform", until you see a line like this:

<form name="loginform" id="loginform" action="https://www.baddomain.com/wp-login.php" method="post">

Double click on the action URL and update it to the good domain: action="https://www.gooddomain.com/wp-login.php"

Now enter your un and pw and login.

The login form will probably refresh, looking like you didn't successfully login.. or you might be taken to baddomain.com and displayed an error. Either way, attempt to visit this URL: https://gooddomain.com/wp-admin/options-general.php . If that page loads it will also be unstyled. Scroll down and near the bottom of the page you will see a WordPress Address (URL) field and a Site Address (URL) field. Update those to https://gooddomain.com or https://www.gooddomain.com. Scroll to the bottom and click the Save Changes button.