I have a KPL and use button D to indicate if somebody is home or not.  I turn button on when leaving  I turn button on and off when  arrive home.  

How can I from program turn that button on or off?

I have ISY 994

1 hour ago, slpelts said:

How can I from program turn that button on or off?

To turn KPL buttons ON/OFF (other than the A button), you have to create a scene into which you add the button(s) as a responder.  Then you simply turn the scene ON/OFF.

Example:

Away status
If
        $sAway is 1
Then
        Wait  1 second
        Set 'Away scenes / Away Status' On
        Resource 'Send away mode change to Stringify'
        Resource 'Away mode status'
        Set Elk Speak Word 'Away'
        Set Elk Speak Word 'Mode'
Else
        Wait  1 second
        Set 'Away scenes / Away Status' Off
        Resource 'Send away mode change to Stringify'
        Resource 'Away mode status'
        Set Elk Speak Word 'Home'
        Set Elk Speak Word 'Mode'
 
Reflects the value of managed state variable "State_Away". 
This is a separate program from "Away mode on" and "Away mode off", 
so that the variable value is indicated at the keypad even if the 
variable value is changed without operating the keypad button, 
e.g., using this client. 
The scene "Away status" contains the keypad button used to turn the 
away mode on/off.