Positive re inforcement of taking to vets and feeding making a fuss etc when calm only, then moving on to taking inside to sit here and again be rewarded when behaving as you want. Problem can be difficult if it is ingrained though patricularly in intelligent dogs.
Pet remedy Kalm aid etc usually make very little difference, sometimes benzo diazopenes can be used to reduce anxiety and prevent memory of traumatic experiences. Speak to your vet who should be able to offer some advice. If not then speak to friends or dog trainers for advice on which vet to go to. Some are just better at handling the more challenging behaviours! I certainly see a lot of them.
Home visits aren’t often much better, just as stressful and away from the back up of multiple nurses and safe sedation if needed. I love home visits for cats. Amazing what you find under people’s beds as you are dragging the cat out from under them!