If you can try to adjust the halter that would be best, they don’t need to be tied for travelling but to ensure things don’t go wrong during loading/unloading it’s best if they wear something so you can easily catch and lead them.
It probably depends on the horse if I’d travel without or just with a neck collar, if they are very well traveled, been there, done that and very unlikely to look at anything or get unsettled I might, but if they are the sort to look around a lot, get worried at new places and start calling out I might be inclined to postpone until the scab is gone.