PCA9685 question

I am able to use servos directly from the arduino
using a Ultrsound sensor.

I add a pca9685 board,
using wire.h
and
Adafruit_PWMServo library
loads just fine, lights up and test code works.
Test code cycles thru them - I dont understand.

How would I only set servo 4 , or whichever, in motion as needed?

Online examples do not explain well enough and I just cant figure it out.

pwm1.begin();
pwm1.setPWMFreq(1600);

from here? where?
myServo4 ??

Thank you.

In the examples that come with that library, it calls the functions with a servonum variable which represents which servo you want to communicate with. If you want to just use the 4th one, servonum would equal 3 (0,1,2,3)

 pwm.setPWM(servonum, 0, pulselen);

THANKS!
I'll try that tonight.
Thank you again.