On a 6-quart Instant Pot, select Normal/Medium Sauté. Add 1 tablespoon of oil and heat until shimmering. Add the couscous and cook, stirring often, until golden brown, 7 to 10 minutes. Using a large spoon, transfer the couscous to a small bowl; set aside. Add the remaining 1 tablespoon oil to the pot and heat until shimmering. Add the garlic and cook, stirring, until beginning to brown, about 1 minute, then add the onion, carrots, bay, 2 teaspoons salt and 1 teaspoon pepper. Cook, stirring occasionally, until the onion has softened, 2 to 4 minutes. Add the cumin and allspice, then cook, stirring, until fragrant, about 30 seconds. Add 1 cup water and scrape up any browned bits. Stir in the chicken, the toasted couscous and 1 teaspoon salt, then distribute in an even layer.