I'll show you four (well, technically five) different ways to do it:
1. Muffle the sound, if you just find it too loud.
2. Disable the sound entirely
3. Add a switch to turn the sound on and off
4. Add a volume knob
The 5th option, which is what I do in the video, combines 3 and 4. Options 1 and 2 require no special tools, but doing option 2 without a soldering iron is not recommended.
Here are wiring diagrams for the other options, with links to where you can buy what you need:
Here is a push on / push off (aka self-locking) switch: https://goo.gl/c4j1r1
You'll need a 20kΩ potentiometer (labelled as B20K), which you can buy here: https://goo.gl/XxgVBD
Volume knob with switch
For this you'll need a 10kΩ (or more) potentiometer with combined switch: https://goo.gl/2WG87b
And finally, here is the video: