I need to know how to get the click onto an exported audio mix. Can someone please help me in this?
You’d have to load a suitable VSTi into the VSTi rack (e.g GrooveAgentOne… with a suitable kit loaded into it 
), then set up the MIDI section of the Metronome Setup dialog, to output to that VSTi. You can then simply export the audio from that VSTi.
You could then save that as a template (i.e. as a starting point for future projects).
Seeing as Metronome Setup doesn’t remember VSTi assignment, better off programming a MIDI track for the click.