Turn on a multi-functional pressure cooker (such as Instant Pot(R)) and select Saute function. Heat olive oil and add onion; cook until translucent, about 7 minutes. Add garlic and cook for 1 minute more.
Combine tomatoes, vegetable broth, basil, salt, ground black pepper, and Italian seasoning in the pot. Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 5 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove lid.