our experienced instructors (old ones, with beard
) teaching newbe, who has problems with breathing underwater without mask, by very simple way. Everybody can do it at own home, on the kitchen (better) or bathroom (not so comfortable).
Just take wash-hand bassin (dishpan), put there enough water (cold, if you planning to have dive at north side, or normal otherwise), and place it on the table in front of you.
Than sit down on the chair, take breathing tube (snorkel or shnorchel, upon your choice), and start to breath from the tube in front of this dishpan. In the air, just sitting in the chair.
Than slowly start to putting down your face in to the water of dishpan. And continue breathing.
Just doing it, without any thinking about water, breating tube etc.
You can listening news or music, during this time... do anything, but only NOT to thinking about what you do. Just breathing.
After some time you will see, that you can do it, when you do not thinking about it
Similar way - when you goes waist deep in water with scuba - just start to breath from mouthpiece and without mask. And slowly start to put your face on the water, and deeper.
You also can do it (later) in neutral bouyancy, swimming in the water on the same depth - where you always can stand on the ground, and take your face from the water.