Downloading from a backup might be easiest, if the backups are kept on the server.
The backup files are usually found in
/var/discourse/shared/standalone/backups/default/
and I’d usually use scp or rsync to copy them to my machine.
Or, on the backup section of the admin page you see a list of backups, each with a download button, which sends you a backup link by email. An admin could cause that email to be sent to them and they can forward the link.