The only way to cure the Ich, completely removing it from your display tank, will be to remove all fish from the display and treat them with either hyposalinity, the tank transfer method or copper based medication. While treating the fish, separately, the display tank will need to remain fallow (fishless) for 8 weeks.
While Garlic has been shown to MAYBE help, with Freshwater Ich (a completely different species), it has absolutely no health benefits in our hobby and has actually been shown to cause organ damage, in marine fish.