How to replace antenna base? 99 Sport

Does anyone how I could replace the antenna and base on my 99 Explorer
Sport?

Recently, it came flying off right in the middle of a drive-in car
wash (yeah, it happens!).

Anyways, I mistakenly bought just the top metal part, but it won't fit
the base, there seems to be a piece of the the old one jammed in the
screw hole.

I gave it a quick try and removed the black plastic cover and found 3
star screws. I took those out, but didn't know what to do next, the
base looks to still be attached to something.