Converting fill into stroke

[MahaB82A]

This is "O" text but expanded. You can see in the first image bounding box is in the ouside of the letter O with a black fill color . I made bounding box is inside the letter by but method is not precise. That mean thickness of the fill area remain the same when doing this convertion. How to do this? file is uploaded as well.

Letter O

[MahaB82A · Accepted solution]

OK I have found. Please ignore this.