In this change ton only one central button, how do we go to the option for contextual menu

for example in other phones where there are 3 buttons, the left button is typically the contextual menu button. While using Apps like Touchdown, this button brings up the settings option, refresh mail option, etc.

I have not yet been able to locate such a button or option (since there is now only one central button which primarily meets requirements of going back or going to home screen only), there are no proper user manual helping here.

Now in Apps like TouchDown I am not able to access the settings options at all :thumbsdown:

Please will anyone have ideas on how to access the Contextual Menu in this Meizu m2 note phone please?