Yes Pepto Bismol is safe to give to dogs with an upset stomach or diarrhea.
You can give your dog 1 teaspoon of Pepto Bismol for every 10 lbs of weight and give the dog a dose of the Pepto Bismol every 6 to 8 hours to settle the dogs upset stomach.
You might also give your dog some Apple Cider Vinegar in their water which can also help them settle their upset stomach as well.
You should also put the dog on a bland diet when they have an upset stomach or diarrhea.
When a dog has an upset stomach or diarrhea you can feed them plain canned pumpkin, a tablespoon or two of yogurt, or probiotics.