Without a schematic or really any basic idea of what kind of pedal it is it’s just a shot in the dark. If you’re using a logarithmic potentiometer try using an anti/reverse logarithmic (C) pot of the same value.
Here's the example. Original potentiometer - 100k, new potentiometer -50k plus resistor with the same (or closest value). Resistor must be before potentiometer.
Signal level with both potentiometers @ max.