Accidentally Changed WordPress URL in Settings>General

Hello,
I am new to WordPress, just installing it yesterday on my Mac. It was all working fine, then I went into my Settings > General and accidentally changed the URL, not knowing what it did. Now every time I go to my localhost:8888/wp-admin/ , it redirects me to the URL I changed it to, and my browser says there is no such URL.
I don’t really have a clear idea on what to do being a first time user. Every form I read, I do not understand…
Please Help! Thanks!