You are talking about “motor slew.” A search here for that term returns How to Program Joystick Channels to Ramp Up in Driver Control - #13 by callen
The basic concept is to created a task that monitors the joystick values and only lets them change by a set amount at a set rate. So, if your driver slams the joystick to 100%, the task only gives them 10% every 50ms – and you adjust the amount and rate until it feels right to the driver.
Alternatively you can run a task that filters the joystick values. There is a discussion of that here: Anybody linearized the motor power yet? - #9 by callen
Warning in advance, those are old topics, do not reply to them.