Try to breath as less as possible within a given time. You will get conscious about your breath. You learn to come along with less O2.
You’ll start with an Apnea phase. When over, press on “Measure” button to switch into a breath phase. When you switch back into a new apnea phase, you press again “measure”. You continue until time is over or you stop the try. At the end, the least breath time will win.
Keep in mind that time measurement is a point of honour. Breathing in is measured as – well – breath. Breathing out is measured as apnea time. That’s why you should try to extend exhaul as long as possible to extend your apnea time.