Do you have a Tandem 2A/2B also?
If so, when your Tandem 2 is scheduled to start, switch out your 1A/1B and just put in a starter 1.
If you don't have anything set up for 2 (ie your entire rotation is just your Tandem 1A/1B) then you have to put a Tandem 2A/2B in for one round - and then use the step outlined above.