unmerging two different solids in CST studio

I have merged two different solids in cst studio and simulated the structure. How can I unmerge (structure before merging the two solids) the two solids and vary the dimensions of the structure?

CST has a history. You can go back or delete the merging step of the solids.

Thank you very much Johnjoe.I have taken Et=0 for Xmin, Xmax, Ymin, Ymax, Zmin and Zmax respectively and no symmetry in all the planes. I have attached port1 and port2 in XZ planes. I am getting two errors while simulating a simple waveguide .They say"when exciting with a plane wave, the calculation domain must contain open boundaries at the direction of incidence" and "port number 1 is completely outside the calculation domain. please remove symmetry or delete port1"(this error is occuring if I am taking symmetry in XZ plane).Please help me out in this regard.
Thank you

Can you post a picture of your simulation setup?