volume button not working

Yes, you can replace the buttons or the button flex (or both if necessary). It will require that you remove the glass/digitizer to access the inside. The iPad mini is one of the more difficult tablets to repair and there are lots of "gotcha's" when re-assembling (which is not covered in the guides).

I would start by looking through the repair guide first. There is no Volume Button guide for the iPad mini but the Logic Board guide will show you how the mini is assembled and the iPad Air Volume Button guide will show you how the button flex is installed (it uses the same flex as the mini).

Take note of what tools and parts you need and then determine if this is something you want to do yourself. Otherwise, look for a repair shop that has a lot of experience with iPad mini's .