Michael,

 

Solution 1.

 

Modify the Help/default.aspx, messenger-user-guide/default.aspx and redirect to your help pages.

 

Solution 2.

Open ChatUI.js.aspx file and modify the following code:

 

function ChatUI_ShowHelp()
{
 OpenWindowAsync(null,"Help/");
}
function ChatUI_ShowMessengerHelp()
{
 OpenWindowAsync(null,"messenger-user-guide/");
}