Migrating individual wordpress sites between multisites

I am trying to create a dev version of one of my ,multsites, which has over 200 sties on it. I need to migrate 2 or 3 sites from this multisite to a new multisite for dev work and I couldn’t find an article on how to do it. Is that because it is really easy to do? Sorry if I am overlooking something obvious.
Thank you very much
Clive