Change main site with a sub-domain in multisite

I converted by single-wordpress install to a multisite install and it set my original site to be the main one (example.com), but that’s not what I want. I want my original site to be one of the sub-domains (originalsite.example.com). How do I move it to a sub domain so I can have a different site as the main page?

I found this, but it’s not explicit how the OP was able to fix the problem.

In what ways do I need to edit the database? Or is there now a more elegant way to do this without having to edit the db?