Volume button not working

@ashokbajaj if you have ruled out any software and settings issues, it could be an issue with either the actual button or a failed power button flex (most likely) I suggest that you inspect the rocker switch and consider changing the flex to fix your phone.

Since iFixit does not yet have a guide for this, use the one from here It was written in Spanish so you may need to use a browser that does the translation for you. Replacement flex cables are readily available at many online stores.

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!