Add chicken breasts, onion, cilantro sprigs and garlic to a saucepan. Add 4 cups water. Bring to a boil. Boil 20 minutes. Remove chicken with a slotted spoon, shred with two forks, and set aside, reserving cooking liquid. To cook chicken in the instant pot, add 1 cup water to the insert of the Instant Pot. Add steamer basket. Place chicken, onion, and cilantro sprigs, and garlic to the steamer basket. Lock lid. Set valve to sealing. Program for poultry. Quick release, remove chicken and shred with two forks. Set aside; reserving cooking liquid.