The peerID is a random string assigned by the signalling server upon joining a game.
You can use PeerIDAt(index) to get the ID of each peer in order of joining.
https://www.scirra.com/manual/174/multiplayer
[quote:b80en4q6]PeerAliasAt(index)
PeerIDAt(index)
The alias and ID of the nth peer in the current room, up to PeerCount.
If you are unfamiliar with PeerIDs, I highly recommend reading and going through the steps of making the Multiplayer Tutorials https://www.scirra.com/tutorials/892/mu ... 1-concepts. PeerID is a core concept and you won't get very far without understanding and working with them.