Use this guide to replace unresponsive volume control buttons in an iPad mini 4 LTE.
This guide will teach you how to remove the volume control assembly which includes: the ribbon cable with the volume up and volume down switches on it, microphone, and volume control bracket. The guide does not detail the replacement of the exterior button covers.
Parts of this guide were shot with a Wi-Fi model and as such the internals may look slightly different from the LTE model. The procedure is the same for both models except where noted.