Connect your Oscilloscope probe to the input channel you are going to use. The process is the same no matter what channel you use. For this demo I will use channel 1.

Connect the probe tip to the Oscilloscope calibration output (typically a square wave output on the front panel). Make sure to connect the probe tip to the signal output and the probe ground to the ground.

Adjust your scope trigger (or use auto on some models) and you should see a square wave as in the picture. The lack of flatness in the response (see circled spot) is what you are compensating for.