I see, sorry, I misread your original message.
You say you have a quiz, is it a Classic Quiz or a New Quiz (or something else)? The image shared is from Classic Quizzes, but for New Quizzes, the moderate page is a bit different: How do I use the Moderate page in New Quizzes? - Instructure Community - 616 - you can tell whether it's a Classic or New Quiz a few different ways, but one of them is that New Quizzes will have the "Build" option before going into making questions (while in Classic Quizzes, it's "Edit").
If it's a different type of assignment, then it may not have a moderate page at all, but you may still be able to allow for extra submissions in their main edit page.