Changed URL in settings and now can't access anything!!

I’m not much of a techy and barely understand what it’s asking me to do.

Then how do you expect to fix the problem?
Please re-read that article and follow the instructions.

Then how do you expect to fix the problem?
Please re-read that article and follow the instructions.

Well I’m not quite sure how to fix the problem, which is why I’m asking…
I have read the article and attempted to do the codes but it is still not working.

For example, first suggestion is entering this code into the wp-config.php file.

define(‘WP_HOME’,’https://example.com’);
define(‘WP_SITEURL’,’https://example.com’);

I searched for the wp-config.php file by entering into my search in my Finder, since I could not figure out where to find it.
I entered it in at the bottom of the file (doesn’t say where I should put it, if that matters), with the options of what my url could be.
Question about my URL – is the it the “localhost” url I’m putting in?
I put in “localhost:8888” which is what it normally was, and the 404 Error did not come up but the page is blank, nothing will load.
Am I missing something?

Unless moved it, your wp-config.php should be in the root of your WP installation