Take 1 cup of yogurt, tie it in a muslin cloth and keep it over a tea-strainer and place a bowl underneath to collect the whey. Keep this inside the fridge. You can make this overnight, so you will have a thick, ice-cream like hung curd next day or at-least make it an hour ahead.
Take grapes, green chili, ginger and cumin seeds in a blender and pulse it 4-5 times. We don't want grapes juice, we just have to mash it.
Add this mish-mashed grapes to hung curd, mix well. Add salt and mix well.