@rogerantho80522 you really can't fix a battery but you need to replace it. Since iFixit does not yet have specific guide for this use something like [link|https://fr.ifixit.com/Tutoriel/How+to+switch+to+safe+mode+on+an+Android+Phone/156087|this video] Now, if there is anything else but a battery question, you have to be more specific about what is going on with your phone.
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!