I agree with JT. If the EC elects a new chair from among its members, I think that resolution would automatically supersede the previous resolution that appointed the previous chair.
In the absence of anything more specific in the Act, I would assume that the EC’s role and power to elect office bearers can be exercised at any properly convened meeting of the EC.
Bear in mind that whoever is the EC chair by the time the next AGM comes around is by default the chair of the AGM unless they are unable or unwilling to chair the AGM.