My gas forced air furnace does not bring heat to 2 rooms on the first floor they are the closet to the furnace and shortest duct work. I no longer use the humidfer that was installed in to the duct work it seems a lot of the hot air is going through the unit can I take it off and have sheet metal put over the holes

Sure take off and cover tightly,as for the no heat in 2 rooms,check or have someone to make sure the duct work hasn`t come apart and heat going someplace else,make sure someone hasn`t closed the vents off

Are there campers in the ductwork? If flex duct, it might have partially blocked the duct. Make sure to duct tape or put mastic over the seams o