Season the chicken thighs generously with salt and pepper. Set an Instant Pot to sauté on high. When the pot registers hot, add the vegetable oil. Working in two batches, add the chicken skin-side down and cook until well browned, about 10 minutes. Remove to a plate.
Add the onion, garlic, carrots, paprika, coriander, cumin, turmeric, ginger and cayenne to the pot. Cook, stirring, until the onion softens, about 5 minutes. Stir in the tomato paste to coat the vegetables, scraping up the bottom of the pot. Stir in the cinnamon stick, preserved lemon, prunes and apricots, then turn off the pot.
Add 2/3 cup water and the olive brine to the pot and stir well, scraping up the bottom of the pot. Return the chicken skin-side up to the pot in a single layer. Put on and lock the lid; make sure the steam valve is in the sealing position. Set the pot to pressure-cook on high for 8 minutes. When the time is up, let the pressure release naturally for 10 minutes, then carefully turn the steam valve to the venting position to manually release the remaining pressure. Turn off the pot and remove the lid.
Transfer the chicken to a platter, leaving the liquid in the pot; discard the cinnamon stick. Stir the olives, cilantro, parsley and vinegar into the pot. Season with salt and pepper. Serve the chicken and sauce over couscous; top with more parsley and serve with harissa.