Just wanted to add, in case some other poor soul, who is a beginner and wants to add a site map finds this thread through search that I was able to access the webftp folder through:
cpanel > manage domain > webftp
location: mydomain [I kept trying to put an ftp addy - but the domain w/o www worked]
and then user/pass.
This is probably super simple stuff, but it had me stymied!
I then uploaded the site map into the general directory or “root domain” (which was indeed named mydomain.com as the user above helpfully indicated) and it worked!
If anyone else has the prob. I did (not likely!) I’m more than happy to help.