Hi albehany, usually you would use object snaps to do that using the Transform > Move command to snap on to the center snaps. But since your target object isn't quite exactly circular (it's possibly a sweep?) there isn't a center snap available on it.

So a couple of options are you could use the BoundingBoxCenter command on the target object (http://moi3d.com/3.0/docs/moi_command_reference10.htm#boundingboxcenter) to create a point there to use as the target point in the Transform > Move command, or you could make a circle using Draw curve > Circle > Circles > 3pts snapping 3 points on to its perimeter edge to make a circle that will have a center snap to target, or also draw a line spanning across it and then use the midpoint of the line.

Please let me know if you still have problems doing any of those.

- Michael