ACV works because it buffers the acid in the stomach and ACV is quite acidic.
Two cups of water when suffering indigestion will fix it and the same, 3x per day, will eliminate it.
People say water just dilutes the stomach acid, which is true as maintaining proper acidity in the stomach is accomplished, by the body, using water. And all ACV does is buffer it - chemically.
Drink plain water. The "water" in food, juice, tea etc doesn't count - it's treated as food and belongs to the colon which the body will simply steal from it when you're dehydrated.
When you're dehydrated, your body has to jump through hoops, rationing water and stealing it from vital systems. Dehydration is an emergency mode that, to handle, requires - you guessed it - WATER. So it's having to use a lot of the little water it is getting to ration and steal/extract it from other the rest of the body. And that's not easy. Try extracting pure water from tea without raising the temp above 99 degrees.
Don't over consume water if you're chronically dehydrated. It can take a couple of years to get the body out of emergency mode and properly hydrated. Plain water is handled differently. It gets snagged and distributed, right now, but it can't do all that it needs to do all at once. If you're chronically dehydrated, that extended emergency mode involves the slow shut down of organs. VITAL organs that get relegated to a "not AS vital" list.
It takes time to reboot and patch damaged organs that have been in the process of being shut down so don't over-consume it but drink plain water. Which is not the same as sucking on a single bottle of water all morning. Drink it.
This is much longer than I intended but no one should have indigestion - nor many other issues - these days as indigestion and all related issues are synthetic "illnesses". You're not sick. You're dehydrated. Many people - including those with indigestion - will swear they drink plenty of water when they actually don't drink much at all. I do not know why.