P.S. if it helps, limiting the footswitch to 1-2 buttons works too (if building/buying a 3-button seems daunting)

momentarily ground the tip and that could be your preset UP
momentarily ground the ring and that could be your preset DOWN
ignore and dont include the third button (n.b. you can press 1+2 at same time and it will act as 3rd switch anyway!)

most footswitches work similar to this but use latching switches…
if you know what you’re doing these could be replaced w momentary SPST switches
but then you’d be mostly building the thing yourself again. (but finding an old footswitch housing does save time and energy)