Looking at the accident report of Ethiopian Airlines Flight 302, it says the cut out switches were used. But the manual trim moved from 2.3-2.1? My reasoning for asking this is because the timeframe on this specific input is 5:40:42-5:43:11 which goes up to the point the crew re engaged the electric trim motors. It sounds like they’re being vague for a reason. Did the First Officer trim in the wrong direction and then tell his Captain “It’s not working”?
On the Boeing 737 the trim wheels are directly connected to the stabilizer jackscrew with cables. The force required to move the trim wheels depends on the load on the stabilizer. The more you are out of trim, the more force is required to move the stabilizer.
From the 737 NG FCOM (9.20.8 Flight Controls - System Description - Stabilizer Trim, emphasis mine):
Manual stabilizer control is accomplished through cables which allow the pilot to position the stabilizer by rotating the stabilizer trim wheels. The stabilizer is held in position by two independent brake systems. Manual rotation of the trim wheels can be used to override autopilot or main electric trim. The effort required to manually rotate the stabilizer trim wheels may be higher under certain flight conditions. Grasping the stabilizer trim wheel will stop stabilizer motion.
The FCTM (8.17 Non-Normal Operations) explains the correct procedure for manual stabilizer trim (emphasis mine):
Hold the control column firmly to maintain the desired pitch attitude. If uncommanded trim motion continues, the stabilizer trim commands are interrupted when the control column is displaced in the opposite direction.
Manual Stabilizer Trim
If manual stabilizer trim is necessary, ensure both stabilizer trim cutout switches are in CUTOUT prior to extending the manual trim wheel handles.
Excessive airloads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually.
Anticipate the trim changes required for the approach. Configure the airplane early in the approach. When reaching the landing configuration, maintain as constant a trim setting as possible. If a go-around is required, anticipate the trim changes as airspeed increases.
Note: this FCTM is from a 737 NG, not a MAX. The part about "trim commands are interrupted when the control column is displaced in the opposite direction" is no longer true when MCAS is active on the MAX, the rest is still valid though.
You can also see this procedure applied in this YouTube video by Mentour Pilot.
Regarding the Ethiopian crash: I don't want to speculate on what the crew did, but if
the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units
then it did indeed move in the wrong (AND - Aircraft Nose Down) direction.