To get “look at” behaviour there’s a second argument to InstantTracker.setAnchorTransformFromCamera which gives various options for the orientation of the anchor that is placed. My post with the original demo contains the best current documentation for this: Instant Tracking WebAR Beta - Example content and API discussion
If you want a placement UI where the content appears at a fixed camera relative position and facing the camera until a “place / lock” button is pressed, then that is accomplished by re-setting the anchor each frame in that placement mode, something like this:
instantTracker.setAnchorTransformFromCamera([0, 0, -5], InstantTracker.TransformOrientation.z_up_y_away_from_user);
When the lock button is tapped, simply stop calling that function each frame, and Instant Tracking will update the anchor position relative to the camera as the camera moves to keep it locked in place.