[Chimera-users] How to model a loop using a template

Dear all, I have installed Chimera on my computer, but I am still new to the program, so forgive me if my question is trivial. I have a nmr structure (completely defined) and a X-ray structure of the same protein, but this last structure has a missing loop. How can I model this missing loop in the x-ray structure using the nmr structure as template (i.e. freezing the x-ray structure and adding only the nmr loop)? I tried opening both structures and using the Tools > Structure Editing > Model/Refine Loop, but if I choose the x-ray structure, then I don't see where to state that I want to use the nmr structure as template. I hope that I explained my problems. Can you help me? Elisa