Got it. Thanks.
I had tried that but my fullscreen.viewModel was out of scope because I was calling it inside a trigger-action that was inside an IdentifyTask.
var viewTrigger = view.popup.on("trigger-action", function (event) {
if (event.action.id === "goto-parcel") {
if (fullscreen.viewModel.state === 'active') {
fullscreen.viewModel.exit();
}
var parid = view.popup.selectedFeature.attributes.PARID;
switchOwner(parid);
}
}); // end trigger-action