Some divers, especially low-quality instructors, usually rush to suggest all manner of easy quick-fix solutions, that don’t really work.
The truth is, your respiration demand is driven by your level of exertion and, thus, how much CO2 your body metabolises.
Fancy breathing methods help expel CO2, but that’s just treating the symptoms, not the cause.
The key to lowering gas consumption on scuba dives is to dramatically reduce your level of exertion.
That’s primarily achieved by improving your fundamental proficiencies: buoyancy, trim, propulsion and control.
When these proficiencies improve, the diver is able to exert proportionally far less exertion on a given dive. They’ll inherently relax and they’ll metabolise less O2 into CO2.. and that’ll reduce their breathing demand.
People avoid that answer because the idea of actually practising and refining their fundamental proficiencies is neither gratifying nor an instant-fix. It demands some self-discipline, patience and a willingness to simply devote your precious time to unglamorous shallow-water dedicated practice.