The Pasts Reminders tab is where you'll find all Instagram posts that were scheduled as reminders (i.e. not published automatically), as well as all Instagram Stories. You can re-trigger push notifications from here if you miss the alert the first time around.
Head to the Past Reminders tab. Here, you can toggle between Posts and Stories.
To re-trigger the push notification to your phone, click Send to Mobile. On the Pro, Premium, and Business Plans, you'll also have the option to Share Again, allowing you to add the post back to your queue.