I have this part this is a currently a molded part.  The are going to make a new mold so I need to remove some material from this 3D part.  It was a parasolid when I imported it into solidowrks.

I need to remove about 0.025" around the inside of the part for clearance with a circuit board.  Highlighted in blue in the image below.

How can I do this?  I was thinking I could do an offset surface or something but that did not seem to do anything.