Your site is currently having a Database error right now so I can’t check it.
To answer your question, make sure that you are naming your file/folder with an underscore “_” and not with a space like this: school_reopening_soon.
The %20 is the URL encoded version of the space character. If you want it to show as underscores, you need to use the underscore character, not the space one.
The database error message looks like one from WordPress. In WordPress, you can change the permalink of a site, so you can change the URL from spaces to underscores.