Rub chicken on all sides with salt, pepper, garlic powder, rosemary, and parsley.
Turn on a multi-functional pressure cooker (such as Instant Pot), add olive oil, and select the Sauté function. When hot, add chicken, breast-side down. Cook until skin is browned, about 5 minutes. Use tongs to flip chicken and brown on the other side for 5 more minutes. Carefully remove chicken from the pot and set aside. Pour in chicken stock and deglaze the pan, scraping off all the browned bits. Turn off the Sauté function.
Place the rack insert into the pot and place chicken on the rack, breast-side up. Close and lock the lid. Select the Poultry setting and set the timer for 28 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. Unlock and remove the lid. Carefully remove chicken to a carving board to rest.
Turn on the Sauté function and whisk cornstarch into the pot with the stock and drippings to make a gravy.