Turn on a multi-functional pressure cooker (such as Instant Pot) and select Saute function. Heat olive oil and stir in onions and garlic; cook until soft and translucent, about 5 minutes. Add carrot, celery, and tomatoes; cook until tender, about 4 minutes. Season with oregano, Italian seasoning, salt, basil, and pepper. Close and lock the lid. Select high pressure according to manufacturer’s instructions; set timer for 25 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. Blend with an immersion blender to desired consistency.