What can I do to fix the volume button back onto my Moto M? Heres a set of pictures depicting the problem.





Any form of help will be much appreciated !!!
Your best option is to take the phone to an Authorised Motorola Service Center to get it repaired, but it may be possible to attempt it yourself. 

As there are no iFixIt guides available currently, your only other option would be to refer to videos a video on YouTube, where the screws on the bottom of the phone are removed to access the internals (and volume button)

https://www.youtube.com/watch?v=9CmvQPpTgfc