but only use it if you will share tips, if not please leave it
The very first thing you should do is increase general exposure and reduce the yellowish color cast. Boost general contrast while you're at it, with an S-curve, and reduce overall saturation.
I see you've used a light tent here, which is normally well suited for jewellery and silverware. However, here you have a direct mirror effect that can be a bit disturbing. In these cases it is often more effective to use a large overhead soft-box played against a dark room. This will bring out the form better, and give more "pop".
A light tent diffuses the light and brings out surface structure at the expense of three-dimensional shape.
To answer the question directly, a mix of clone stamp and healing brush should remove the central black area.
I'm sure someone will have a crack at it, I don't have time now...
the problem is not just in center spot, there are many marks on the piece that need to be cleaned out
are you trying to make it look like brand new?
if so. i would rather remake it.
you would benefit form watching this:
Bert Monroy tutorials would teach you everything you need to know to remake that in photoshop.
Or you can spend hours using the heal/clone tools. with other tools..
Like D Fosse said a mix of the Healing Brush and Clone stamp should tackle the central black area.
This vid might help to produce a more overall consistent colour: Photoshop Tutorial & Best Hi-End Jewelry retouching tutorial. - YouTube
Hope this helps!