The video shows the steps to do the alternator test for the 6100P automotive code reader.

1.Engine need to be running at normal temperature,start engine and turn on headlight
2.Increase engine speed to 2000 RPM AND hold it （20 Seconds）there until the contdown reaches zero
3.turn the headlights to the off position and return engine to idle speed.

After completing the above steps, you will get the test result immediately.

Warm tips: don't perform this test on smart alternator,hybrid and electric vehicles.

What Signs Indicate a Weak Alternator?
Before you test your alternator, here are some signs that your alternator might be weak:
Your battery light is illuminated on the dashboard.
Your engine is cranking slowly or won’t crank at all.
The battery, headlights, and/or interior lights seem weak.
The alternator is making rumbling or squeaking sounds.
You’ve tried and failed to jump start your car.
The above symptoms could also be signs of a weak car battery.

You can get it here:
https://amzn.to/3srhlXx
With a 20$ coupon