Musicbox, TTSGPIO - Variable resistor for volume control?

Hi, thank you for your help in advance!

I have successfully set up mopidy, music box, music cards and ttsgpio - but for the final element of my project, I am keen to try and control the volume with a variable resistor (typical volume nob) instead of a single button for volume up and a single button for volume down. I am relatively new to raspberry pi, but imagine there is a script I can insert somewhere and relate to a GPIO pin. The difficulty is I am not entirely sure what that script would be and where I would need to insert it.

Would be extremely grateful for any help on this.