Tags onUpdate

[GreyFox777]

Can someome explain me how to update the tag onUpdate?

-- PVP Timer
tags['myaddon:pvptimer'] = function(self, elapsed)


local sec = math.floor(GetPVPTimer()/1000)
		if( GetPVPTimer() >= 300000 ) then
			return nil
		end
		
		return string.format(GetPVPTimer() / 1000)
end