Entered Incorrect URL now getting 404 Error Code

I was trying to change my site to a different url and entered the incorrect address. Now I can still login from my previous wp-login.php but after I do I get a 404 error code.

I would like to know how I can just return the site to its previous state on the old url.

I have looked at previous posts but I am not too tech savvy and dont know how to enter the lines of code that seem to be the fix.