WordPress Multisite (sub-directory based), change subsite URL

If you go to your Network Admin -> Sites menu, you should be able to edit the site and change the site’s Site Address (URL) to whatever you need it to be.

As for the search/replace: I recommend using WP-CLI’s search-replace command to do this, if you’ve got it available.

wp search-replace https://example.com/site-1/ https://example.com/site-2 --url=https://example.com/site-1 --dry-run to see what will be replaced, and then run it again without the --dry-run argument to actually do the search/replace.