Why can’t one of the remaining three be chairman?
In any case you can ask your strata manager to act in any or all of the office-bearer roles … but they will quite rightly charge you fro the privilege.
Why don’t you ask one of your tenants if they want to come on (although you will have to get a non-member owner to nominate them)?
Next AGM, reduce the numbers on the committee to 5 or 3.