Peel and cut the potatoes into 1-inch cubes.
Start the pressure cooker in Saute (Normal) mode and let it heat. Add oil, cumin seeds, green chili pepper and minced ginger. Saute for 30 seconds.
Add spices. Mix them well with the oil and cook for 30 seconds.
Add potatoes, water and stir well. Press cancel and close lid with vent in sealing position.
For instant pot, start on Manual/Pressure Cook mode at high pressure for 1 minute. When the pressure cooker beeps, press cancel and release the pressure manually.
Whisk the yogurt and keep it ready. Start the instant pot in Sauté mode. Add yogurt while stirring. Keep stirring gently until the curry comes to a boil in about 3 minutes. Then turn off the pressure cooker. Add salt to taste and stir it.
Garnish with cilantro. Potatoes in yogurt sauce are ready to be enjoyed with roti, puri or pulao.