Stir yogurt, lemon juice, turmeric, garam masala, and ground cumin together in a large bowl. Nestle chicken thighs into the yogurt mixture and turn to coat. Cover with plastic wrap and marinate in the refrigerator, 1 hour to overnight.
Combine water, rice, and salt in an electric pressure cooker (such as Instant Pot(R)). Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 6 minutes. Allow 10 to 15 minutes for pressure to build. Release pressure using the natural-release method according to manufacturer's instructions, 10 to 40 minutes.
Heat oven to 250 degrees F (120 degrees C). Transfer rice to an oven-safe bowl; keep warm in the oven until ready to serve.
Melt butter in the Instant Pot(R) on the Saute function. Add onions, ginger, garlic, and cumin seeds. Saute, stirring frequently, until onions are softened and translucent, about 7 minutes. Stir in tomato paste for 1 minute. Add tomatoes, chile peppers, and cinnamon stick; cook and stir until chiles are softened, about 10 minutes.
Place chicken thighs, marinade, and chicken stock into the pot. Close and lock the lid. Select high pressure according to manufacturer's instructions. Cook until chicken is no longer pink at the bone and the juices run clear, about 20 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure using the natural-release method according to manufacturer's instructions, 10 to 40 minutes.
Transfer chicken thighs to an oven-safe bowl; place in the oven to keep warm. Switch pressure cooker back Saute function; bring sauce to a boil. Cook until reduced by 1/3, about 10 minutes. Stir in coconut milk; cook until heated through, about 1 minute.
Scoop rice into each bowl; add 2 chicken thighs. Ladle sauce over it all and top with cilantro.
