@teohchingyeong since iFixit does not yet have a specific guide for your phone, use something like [link|https://www.youtube.com/watch?v=ta36IPUeiks|this video|new_window=true] to replace your phone's battery. This is for the ROG,if you have a version 2-6 etc, let us know since those instructions can be different.
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. [link|https://ifixit.com/Guide/new|https://ifixit.com/Guide/new|new_window=true] The iFixit community will appreciate this. Repair is War on Entropy! https://www.youtube.com/watch?v=ta36IPUeiks