The best way to do this would be iPaaS by allowing it to use the APIs to create a ticket into the other instance with credentials that have been securely provided.
Outside of that, you'd have to have either a web service method step that makes a call out to the other instance, or else a self-created system that could execute a script making an API call to the other instance when a webhook was received for a ticket that was marked in some way as needing moved.
In any of those options, you'd have to have a valid set of user/service account credentials that could make the API call to their endpoints for ticket creation.
It wouldn't be a true "move" of the ticket, only a creation of a ticket in their instance using information from the ticket in the current instance.
Sr Support Consultant, CS