I need help with rounding the top of my custom helmet

I decided a little while ago to design a fiberglass helmet so I have something cool to wear for geeky events. I designed it and took measurments of my skull, then I added about an inch for more room. I have made an extrude and also have made an extruded cut for the general shape of the helmet. After this I tried to make a constant radius fillet, a full round fillet, and a face fillet to round off the top, but it won't let me. I could use some help with this. I have attached the parasolid and standard files to the bottom in a .zip.

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