we'll assume you're using the stock radio:

i recommend picking a gyro mode to fly in and sticking with it (ie rate vs hh) . although the cp pro tx allows remote gain adjustments, it is only useful for adjusting gain within the same mode. to elaborate on this, the stock tx cannot switch from hh to rate mode in flight because it lacks "conditional revo curves" found on programmable radios that make it possible.

for hh mode on the g90:
bzinfinity is correct if you are using only hh mode on the g90. if you are not flying in rate mode, turn the proportional all the way counterclockwise and leave it there.

for rate mode on the g90:
if you are using "Rate mode" on the g90, some form of revo mixing MUST be used. if you have a stock tx, you must add "revo" using the proportional trimmer on the 3n1.