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 Share Again and then select Share Now. You also have the option to re-add the post to your queue or schedule it for a custom date and time.