I know it is difficult to describe. You don't have to hold you nose shut. It is a minor player in the process. I will try to describe the process as if I am doing it.
Seek a quiet place, stand or sit, your choice. Start by inhaling slowly, ignore your nose. Inhale until lungs are full and immediately start exhaling until lungs are empty. (At end you will need to push the air slightly.)) Immediately start inhaling again. That is what I mean by keeping a signal going to your diaphram. And it does take some practice. Repeat inhale/exhale one more time and end on an exhale. Just relax, don't breathe 'til you need to. Just sit (or stand.) If the hiccups are still with you, give it a few minutes before you try it again. I have never had them last through more than two rounds. Glad to answer more questions if you have them.