I noticed the prop pitch levers seem to have fixed positions like in the BF109E-3. Pressing the two-way rocker switches to
Größer, the RPM increase , by pressing
Kleiner RPM decrease. The original switches return automatically to neutral. Please have a look at chapter 7.o4 in the JU88A-1 Betriebsanleitung from 1940:
Happy landings
Varrattu