How do I remove /blog from main site in multisite install?

As I went to port my existing site to a multisite, I discovered the core site permalinks get /blog inserted into the links, which I can’t have happen. So – I have looked up everything I can about it and nothing works. I just installed the multisite a few days ago. Do you have a tutorial on what I can do to have a flat URL permalink ( for my core site posts? Thank you!