If you're on a Team plan but aren't the Team plan owner, you can't publish new prototypes for your team from Craft Sync—you can only sync to existing prototypes you're a collaborator on.
To sync to a new prototype, you will first need to create a team prototype in InVision Cloud. You can then return to Craft Sync and sync your Sketch or Photoshop file to that prototype.
If you're the Team plan owner, new prototypes will always be published to the Team plan. This can't be changed.