General secretary not doing their work in apartment

You have to check the bye laws of your society, if there are no bye laws then simply make a resolution and  dismissing the GS and appointing another to be signed and voted by all of the associates/members.

In case the General Secretary is not accepting to resign and what is process to do legally?

You have to dismiss him. Just make the resolution and isue notice of dimisaal to him , he should be warned of legal consiquences if he acted as GS after dismisall and 

Who will make a resolution in our apartment Management committee? President? any sign required from MC members?

The MC and the President shall approve that, you must go through the bye laws if you any;