[phenixbb] how to make covelent link of BME with Cys and refine

Hello Sabine Yah i could specify link in the pdb and also could see it in coot but when i go for refinement then bond is broken. I given pdb mtz and cif files in refinement. The only problem i feel could be that i don't have restrains for SS bond in cif file but i don't know how to generate SS-bond restrains. Thanks RAJ