Set Gizmo to middle of object?

Hi guys.

I am working with brushes atm.
I transformed a box via geometry editing (F5) into a small wall.
Now I am searching for a solution to bring back the gizmo into the middle of my box - permanently.

All answers i found to that problem are not permanently.
If I choose another object and go back again, the gizmo is right back somewetre else.

Can someone help plz?

Really no answers?