Changing the directory…Help!

Don’t touch those URI values if you don’t know what are you doing. That should be rule #1.
#2. Always read the docs before doing anything: https://codex.www.ads-software.com/Giving_WordPress_Its_Own_Directory
#3. To get out of the trouble: https://www.tamba2.org.uk/wordpress/site-url/

Thanks, I’ll try that.

Will using that third link allow me to login again? Because I can’t follow that second link’s instructions unless I can access my blog, right?

Yeah, sorry about the wrong order.
Go first to #3 to fix your problem and then try to do what you wanted in the proper way.