Either the wp-config.php will exist in the same folder that WordPress was installed to, or it may be located one level above your install folder.
If you have access to the server backend by use of an FTP client (“File Transfer Protocol” client), once logged into your FTP session, you can navigate to find the wp-config.php – and then select to “edit” it as a text file downloaded to your local computer. Once you have added the two lines I mentioned, simply save it – and then upload it to replace the original file on the server.
The only other means I could help, is if you had access to any kind of database manager (like PHPMyAdmin, for example) on the server your website is hosted on. Then here is where you would find the entries for your site’s urls – and make the changes to the contents of those database fields.
If this is your website, or you have the authority or responsibility to access the “control panel” features of the server (IE: Being able to log into the server backend control panel), then here is where you will need to access the database manager, so that you can make the corrections in the database records.