How can I delete an incorrect domain name from the URL

I need to change the URL back to the default Squarespace URL, https://flute-tomato-z39m.squarespace.com/

I can't change the incorrect domain name I entered in Marketing SEO & URL.

The domain part of the URL is greyed out, so I can't delete it or change it.

If I delete Marketing, will I still be able to add it in later?