@stephenousaban if your battery does no longer work, replace it and then re-evaluate. Since iFixit does not yet have a specific guides for this, use something like [https://www.youtube.com/watch?v=OUz9fJ6Y8GI|this video] Replacement batteries are readily available at many online stores.
If your phone has other issues then having to replace the battery, you need to be more specific with your question.
While you work on your phone, 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!