That depends on what state they left it in. You could try to go through the rails console:
cd /var/discourse
./launcher enter app
discourse backup
cd public/backups/default
scp * user@destination.example.com:
Your backup filename has the format forumname-2025-05-22-151843-v20250521053324.tar.gz
The long string at the end is the latest migration that has been ran.
To find out which commit it belongs to,
cd /var/www/discourse
git blame db/migrate/20250521053324*
You will now see some output and the left column contains the commit hash.
This is the minimal commit your new forum should be at.
(Sometimes the commit belongs to a plugin, in that case use locate to find the plugin, cd into its directory and do the same git blame stanza)