Hi anon, don't panic. It is not a big deal when a dog is stung by a bee or wasp. Made a paste from baking soda and water and apply it over the entire area. To reduce the swelling, apply some ice to the area for about 5 mins (you can remove it from time to time to prevent discomfort from the cold). You can also consider giving your dachshund some histamine antagonist if you think that the swelling is too big.
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.