You have two physical passes, but want to change them both to be printable passes instead. With the physical pass, you are able to add additional items, but you can’t with the printable pass.
If each printable pass has a different unique indicator which needs to be displayed on the pass (Printable Pass Number in the Setting), then you would need to create this pass as two separate museum records with one item assigned to each. If not, then you can have one museum record with two items assigned to it.