The PlyPlayer contraption exposes a .passage attribute which is read/write. To set a PlyPlayer named "player" to a passage named "Mailbox" you'd simply have a script like
player.passage:"Mailbox"
See the documentation card for this contraption.
i see. thank you!
since we're on this subject, how would you suggest to store the last visited passage so i can make, say, an inventory button to take me to a passage outside of the story path and then take me back to where i left off? i tried making a grid of visited passages but it got really messy...