Easy(ish) way to switch primary site

I have a multisite install(built on subdirectories,not subdomains).

On my primary site is the “old site” and a subdirectory is the “new site”. I want to replace all the content,posts,theme,etc,on the new site to the old site.

In summary

The old site https://www.mysite.com now needs to have everything that https://www.mysite.com/newsite has on it now

I know that primaries cannot be redirected because of the obvious,so what is the best way to do this and would I need to change the entire configuration?

Also,i have the “blog copier” plugin installed,but it will only install on yet another subdirectory which won’t really accomplish this particular task.