The way it looks to me:
Take the original 47uF and substitube a .68uF cap instead (probably film).
OK, now, from the gain pot wiper (which also connects to the .68uF cap), run a wire to a 2nd 5K pot wiper. Then take an outside lug of the 2nd 5K pot and connect the 1uF cap to that.
Now, take the other leg of the 1uF cap and either connect that to the back of the 2nd 5K pot back, and then that to ground OR connect it directly to ground. In any case, ground it.
It sounds to me like he just replaced the 47uF cap, with a .68uF film cap and is blending in another 1uF of capacitance for a total of 1.68uF of capacitance.
Does that make sense to you?
Let me know if you have questions.