Changing the domain name is fairly easy but swapping one site for another site as primary is right involved. As far as I know, there’s no plugin. It can be a perilous task… I have done it.
My advice would be to not do that… I use a dedicated domain name for my primary network site. With domain mapping built-in you can use a subdomain even as your primary… I like calling my network primaries as ‘NOC’ dot domain name now.
Anyway, here’s a StackExchange answer about that process if you wish to try it.
https://wordpress.stackexchange.com/questions/232038/switching-primary-site-in-wordpress-multisite/235578
Read up on it well and do a backup first and consider may be using a new multisite instead, just changing the domain name instead, and/or migrating the site using the primary to a subsite instead.
-
This reply was modified 4 years, 1 month ago by JNashHawkins.