@stevie yep 10k res from top of C19 to bottom of R16, or via switch, or variable by a pot?
Not 100% if it brings it back to flat, i think it more reduces the amount of scoop based by the existing circuitry, rather than actually boosting the mids.
Result to the ears may be similar...
5 mins and pence job for adding the resistor to the board, no wire, no switch, no holes, easy reversed...