[modeller_usage] to model heterodimer protein of mossing residue

i tried a build a homology model of a heterodimer protein,since it contains missing residue i have to model that. But i am only familiar with single chain homology modelling and fro multi chain i am getting many errors like in greeting ali flie. and from tutorial also i am not getting everything clearly. can i get a detailed explantiojn on multi chain modelling