Lost zero-ing tool for TA041 active probe

[ocset]

Hello,

We have lost the little screwdriver which is needed to zero our  TA041 active probe.   
None of our standard screwdrivers seem to work with it. I shone a torch down the screw hole but cant even see what type of head the screw is.
Do you know a part number for the screwdriver which adjusts the zero-ing?

TA041 active probe.
https://www.picotech.com/accessories/high-voltage-active-differential-probes/25-mhz-700-v-differential-probe