Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Lhasa Apso, watch their eyes, their back and their water bowl. For squinting, a watering eye or pawing at their face, contact your vet now, because an ulcer can get worse quickly. Yelping when picked up, a hunched back or wobbly back legs can be their spine. Drinking much more than usual can be their kidneys. And growling at their own family is never just them being a Lhasa. Bloat (GDV, a twisted stomach) can happen in any dog, though it is most common in large, deep-chested breeds. A swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling is an emergency: contact your vet now.
They'll keep reporting every courier. If they ever growl at you, tell your vet.