On 6-quart Instant Pot™, select SAUTE; adjust to normal. Melt butter in insert. Add onions, salt and pepper; cook 6 to 8 minutes, stirring frequently, until softened. Select CANCEL.
Stir in ham, carrots, celery and garlic. Stir in broth and water, then stir in peas.
Secure lid; set pressure valve to SEALING. Select MANUAL; cook on high pressure 15 minutes. Select CANCEL. Keep pressure valve in SEALING position to release pressure naturally. Stir; let stand 10 minutes.