How to reset the Watchdog?

I just enabled the watchdog in bios on LattePanda 3 Delta. It successfully re-starts the system after the set time delay. 

But: How do I re-set the watchdog timer? I tried sending a square wave to the WDT-pin but it did not work. 

I can't find any documentation on how to use the feature correctly. Please point me in the right direction. Thanks!