WordPress droplet - locked out of wp-admin page
I have a DigitalOcean droplet for WordPress. I set up my website, but then went into General Settings and changed the Site Address URL and immediately became locked out completely. All I can see is the error 404 message every time I try to reach my admin page.
I've seen online there are suggestions to update the wp-config file with the following:
However, I do not know how to even access this wp-config. I am very new to all of this, so if anyone has any step-by-step instructions that would really help!