Please see attached document.
To retrieve a particular help topic ID, in the Author Client Help (CHM), right-click the topic and choose 'Properties'. In the 'Properties' window for that Help topic, place your cursor in the Address (URL) field and hold the left mouse button down as you drag the cursor right. This will reveal the end of the URL, where the help topic ID is found. In the example attached to the solution called 'Properties', the help topic ID is ‘actionregistry’.