FIRST, NO PEOPLE FOOD, PERIOD!
If your dog thinks it is okay to steal food from a counter or unattended plate, that’s not okay.
Your dog must always sit and wait for his food. No free feeding!
Get yourself a plate of food, even if it’s just snacks, and have another family member hold the dog on leash and every time he moves toward your food, a correction and a stern “leave it”
You need to teach him the leave it command and it’s very easy to do. Have a high value treat in your hand, made into a fist, let him smell it, he will try to get it, keep saying “leave it” until he stops trying to get it (disengages) and turns his face away from your hand. Then say “good leave it” or “good [name of your dog]” and let him have it. Timing is KEY so you have to give him the treat within a second of the time he stops trying to get it and turns his face away from your fist. Several repetitions of this 3-4 times a day and he’ll have it in a day or so!
Your dog must know that the food is yours and that all good things come from you and you are sharing because you are the leader!
Remember, a little spit in your dog’s food goes a long way to establishing yourself as the pack leader!