First, you’ll need an FTP (File Transfer Protocol) client to connect to the web server on which your site is hosted. If you use a Mac, you might try Transmit or CyberDuck. If you use a Windows PC, you might install SmartFTP or WinSCP. An FTP client allows you to connect to your web server and browse the files on it, plus transfer files between the server and your computer.
Connect to your web server using the FTP client. You will need the FTP login information, which should have been furnished to you from your web host when you created your hosting account. If you don’t know your FTP login information, then you can ask your web host for support.
The wp-config.php file is usually located in the root folder of your website with other folders like: /wp-content
To edit the wp-config.php file, simply right-click on the file and then select download from the menu. Your FTP client will then download the file to your computer. Then, you can open and edit it using a plain text editor program like Notepad or Text Edit.
Remember, when you’re finished making your changes to the file, you’ll have to then upload the newly-edited file back to your web server, overwriting the older file.
It’s always a good idea to make a complete backup of your website and a copy of the wp-config.php file before editing it, as it contains critical information about your website. An error in your wp-config file could result in your website crashing. Take care!
Hope this helps!