If it was a bee, you have to remove the stinger before doing the above. Try to look at the swollen area carefully and see if there is a sting. If you locate it, remove it with clean tweezers. Make sure you pull it straight out so that the stinger doesn't get broken off. If you can't find the stinger, apply the mentioned paste anyway, it will help neutralize any toxins that your dog got.
As I've said, it's not a big deal. Dogs often get stung by bees or wasps because they love running about and rolling over on the grass. It's only dangerous when the canine is stung in the nose, tongue, mouth or head since it can cause breathing problems. In this case, veterinary aid is a must. It is also a must if the area is swollen too much and it does not seem to get better.