How can I model a homodimer when I only have the PDB of the monomer

Hi,
I have a domain swapping protein 2ilk(A),it can assemble into homodimer(A-A).I want to use a linker to connect the homodimer(A-linker-A), and use I-TASSER to predict the structure.But the result of the last job is not the biological assembly of protein A .
I use 2ilk as the template ,but the PDB file contains only monomer sequence(A).I want to know how to specify template alignment and restrains to get the correct form of dimer.
Thank you very much!