@omarwannahike REI unfortunately does not have a sleeping bag washing service.
The good news is that a synthetic bag is way easier to wash than a down bag! Here is a really good video that might help!
Also using a sleeping bag liner will also be an option that might help out in the future. I'm not sure "how" your sleeping bag is dirty, but if it is because of dirt and oils from you body this will help! It is easier to wash your sleeping bag liner than your sleeping bag!