Relevant information is available both at the Kiev Survival Site and in Isaak S. Maizenberg's book All You Need to Know About Design and Repair of Russian Cameras (1996). The screw you mention is used to calibrate the galvanometer scale. Of this, Maizenberg writes:

To shift the galvanometer's scale, insert a screwdriver in the screw slot [...] and slightly turn it. If the screw does not turn, you should somewhat loosen the nut that is fixing it, and tighten it after the adjustment is completed. The galvanometer's scale should be shifted by small amounts. (p. 283–284)

(This is actually in connection with discussing the Kiev-3, but as he notes later on in the book, the advice applies equally to the Kiev-4.)

Maizenberg also says that

[i]f the exposure meter readings deviate from the real value by over 50 percent, the meter should be adjusted with the aid of the calculator. (p. 284)

The calculator is the round part on top of the camera, and its disassembly is covered by Kiev Survival Site (see link above). But from Maizenberg's writing I take it that <50% adjustments can be carried out using the galvanometer scale fine-tuning screw alone.

Having said all that, a 10% difference is likely to be entirely negligible, at least with negative emulsions, and I'm not sure a selenium meter's accuracy is much more than that to begin with (?). Anyway, it should be an interesting exercise to see if the meter can be calibrated against an external standard using the screw alone, as this is a non-invasive procedure. I'm not sure I would go to the trouble of disassembling the camera unless the meter was widely off (by several stops).