Looking at the traces on the PCB, you can see that the cap(s) in question is/are the output cap(s).
The 4µ7 will let more bass out of the pedal, 220n will be tighter in the bass.
If you already have a bass-heavy signal path from guitar to amp, you might favour the 220n, whereas a Tele through a tubescreamer into a nasal amp, well you might very well prefer the larger 4µ7. If you play bass you most likely will prefer the 4µ7 — definitely socket and see which you prefer and if you find yourself still on the fence, then stick both caps on an on-on SPDT switch (or DPDT on-on) and have either option at your command.
You could even go hog-wild and have a DPDT on-off-on with three caps for three settings, splitting the difference or going even bigger.
Split-the-difference:
4µ92 UP (4µ7 in paralled with the below middle cap)
220n MIDDLE (across lugs 2 and 5 of the DPDT on-off-on)
2µ42 DOWN (2µ2 plus the above middle cap paralleled)
BASS!
4µ92 UP (4µ7 in paralled with the below middle cap)
220n MIDDLE (as described above in "split-the-difference")
10µ22 DOWN (10µ cap paralled with above middle cap)
Call the switch "character" or whatever...
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