I wooted a few of these dandy devices a while back and they work great but the volume buttons are weak and the solder points easily break loose and let the buttons fall inside the case.
You may also find this helpful with other simple repairs such as leads that have broken loose..
A few basics you'll need:
Soldering iron solder and flux
Small blade or standard screw driver for leverage
Step 1: Removing Ear Clip **Optional Step**
The first thing I started with was removing the ear clip by simply pulling it off.
This is not required to disassemble the unit but I found that it is easier to handle without the ear clip.
Step 2: Lift Away the Front Cover
The front cover is not easy to pry up despite the fact that it is only attached with sticky tack. Start at the back of the unit near the USB connection. There is a small indentation where you will want to get under the cover.
**An Important Note**
The blue foil backing is very delicate and if you are not careful you can mare the smooth appearance of the foil. For best results alternate lifting each side little by little until it lifts completely away.
Step 3: Remove the Screws
There are two torque screws that will need to be removed before you can open the case. I think they are T5 but the smallest I had was a T6 so I cheated a bit and used standard 1.5 tip.
Step 4: Pop the Case
With both the screws out the case will very easily pop open from the side with little effort.
Step 5: Make Some Working Room
The lead wires are long enough to pull the board out far enough to let you do most any repair that you need with out the need to break the glue bond holding the mic, speaker and other components mounted inside the case.
If you really feel the need to disconnect the board completely the solder pads are decently sized so you don't need to be an expert to work with this one.
Step 6: Preparing to Reattach the Volume Button
As you can see I have pulled the cover back to give me easy access to the area of board the volume button will reattach to. Everything is easy to get at and my soldering iron is heating up.
Step 7: Place Volume Button
Tweezers are very helpful with placing the button into place. There are plastic pegs on the back of the button that help it stay put while you solder.
Step 8: Solder Button in Place
Nothing special here, simply hit the solder pads on each side of the button. With any luck that is all that you are going to need.
Alternatively if the issue was a loose lead or something similar then repeat as needed, it should be pretty straight forward.
Step 9: Reassemble
From there you should be good to go. Simply reverse the disassembly and you will be set.
Worth noting is that the exterior volume button literally balances on the edge of the circuit board and actual volume buttons. Also the volume up button is towards the speaker and the volume down is closest to the mic, so make sure you get the orientation correct.