Decibels conversion into amplitude ratio
You will want to work with what Wikipedia calls "field quantities."

Your engineer is telling you to work in steps of .1dB, which would be an amplitude ratio of .1=20log10(x).  To get x you do 10^(.1/20) = 1.01158

From x dB to ratio (amplitude):  10^(x/20)

From x ratio (amplitude) to dB:  20Log10(x)

If you can calculate the ratio, then you should be able to calculate the correction needed, round to the next .1dB step, and apply it in one step.