@anthony88202 iFixit does not yet have a specific guide for this. There is a great teardown right here [guide|151606] and if you combine that with something like [https://www.youtube.com/watch?v=hNMrxdgT7CQ|this video] you can do the battery replacement by yourself.
While you work on your Fitbit, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.
Repair is War on Entropy!