Full disclaimer that this might be common knowledge!
Short v - warm up some water in the microwave, doesn't need to be hot at all- take some sips, no need to down it or rush.
I had really deep painful hiccups a few weeks ago, couldn't clear them by holding my breath, drinking a drink fast etc- had a quick look on tik tok and a woman said drinking water warmed up in the microwave clears them straight away- I tried it and instantly my hiccups were gone!
I've been waiting to get them again since tk make sure it isn't a fluke, DS 6 has just had them and sure enough, warmed up water cleared them after just a few sips!