KA03 progressive acceleration and deceleration

Hello, I am controling 2 DC 12 volts motors with the KA03 and it works fine with the sketch example.
I want to have progressive acceleration and deceleration. How to do ?
Thanks for reply

You will need to write some code that generates a PWM signal of which you can vary the duty cycle from 0 to 100%, in order to adjust motor speed.