Set the Instant Pot to saute(more) mode and heat oil. Add mustard seeds in the oil and allow them to pop which may take 2-3 minutes. Add onions and sauté for 2 minutes.
Add turmeric, green chilies, ginger, and curry leaves. Saute for 30 seconds. Press Cancel. Add potatoes, salt, and water. Mix well, deglazing the pot if needed. Close the Instant Pot lid with pressure valve to sealing. Pressure Cook for 4 minutes followed by quick release. Turn the Instant Pot off.
Open the Instant Pot lid. Add lemon juice and cilantro. Mix gently and enjoy hot.