Select your preparation time to get ready for the training session. A good value is 2 - 3 minutes to do pranayama breathing, reduce your heart-rate and mentally prepare for the training.
Choose a breathhold time where you can comfortably hold your breath: A good value is 60-70% of your maximum breathhold time.
Choose a recovery time that allows you to hold your breath for the same time as you did before. 1 minute is a good starting value.

Set either an increase for your breathhold time (start with 10 seconds) for O2 Training
or set a decrease of your recovery time (start with 15 seconds) for CO2 tolerance training.

Select 8-10 rounds.

Tap "start" to begin your training session.

Never hold your breath under water without a qualified person supervising you and without proper freediving training/certification!