Building crystal

Hello, 

I'm fairly new to Materials Studio and am simply trying to building a 56 atom platinum cluster. The space group is FM-3M, and Pt's lattice constants are 3.9242 Å. I know I need to build a supercell and unbuild the crystal to carve out the cluster, but when I go to rebuild the crystal, the "rebuild" option is not there. I then have to build the crystal and input all the information, which gives me a completely different-looking cluster than what I just built. Any help would be greatly appreciated. 

Best.