First you need a inspiratory muscle trainer device and nose clips/plugs. It's basically just a valve that can be tightened with a knob. You can get them on Amaz

First you need a inspiratory muscle trainer device and nose clips/plugs. It's basically just a valve that can be tightened with a knob. You can get them on Amazon and whatnot. The actual exercise just involves inhaling through the device, for a couple of minutes, and over the course of days/weeks/months working up to higher resistance levels. It's hard work, and it bugs me that it forces you to mouth-breathe, but it will strengthen the muscles. The linked study does 30 inhalations per session.