The Android MENU button is found in various locations, depending on which  device you are using. Here's a link to a great article on how to find your MENU button from the folks at WhatsApp.

Where is the menu button?

The MaxMon app also has a three horizontal line icon (≡) at the top of each screen. Pressing it has the same effect as pressing the MENU button (while in the MaxMon app - it brings up a menu of options for that app screen).