Arduino Robot wheel calibration by rotating TRIM

Hi! I am working on Arduino Robot. I came across the following way of Wheel calibration:

As per the schematic I see that the TRIM value goes to the microcontroller via AD3/ TRIM. However, I am unable to find that how this AD3/ TRIM value affects the Motor speed. I see only IN_A1, IN_A2, IN_B1, IN_B2 as inputs to Motor Driver DRV8833PWPR which has no connection to AD3/ TRIM. Also the wheel calibration code does not do anything to write the TRIM values to IN_A1, IN_A2, IN_B1, IN_B2 to change the Motor speed.

I am wondering how the change in TRIM value changes the Motor speed. Does anyone has any clue on this?

Probably the Robot code calls Robot.trimRead() and uses it to modify the motor drive level ?

It may not be really changing the speed. What it might be doing, is adjusting the distance estimation for how far the wheels have travelled. It is hard to tell without looking at all the code.