I bring up the existing documentation, and have them run through it mostly on their own with me sitting there, asking me whenever they have questions. I watch over their shoulder and nudge them if I see something going awry. They jot down notes that they'll use to update the documentation later. Once they're up and running, they ping me whenever they get stuck, and then jot down notes for the documentation later.

The important part is that they read the docs (as a sanity check that the docs still make sense to a newcomer) and perform the actions themselves. I don't touch the keyboard except when it's a complicated, exceptional issue that they're not expected to deal with at this level.

The other important part is that they update the documentation.