How to set "Stress Low voltage" parameter at AC Voltage Stress in Clarius 1.9 or latest version

Hi, everyone

I'm using the 4200A-SCS, for stress testing.

Subsite Operation = Stress
Stress Mode = AC Voltage
Device = diode (or whatever)

One Terminal PMU1-1
stress voltage = 10V
Duty Cycle = 50%

Terminal Settings
Force Part
Stress = 10 V 
Duty Cycle = 50 %
Stress Low = 0 V  <<<--------- This part not editable. just fix value 0V. I want to this value to 0.5V or -0.5V or -1V or whatever

How I can edit "Stress Low" parameter value?

Please, help me