Hello Lilly5589,
Thank you for reaching out in Apple Support Communities. What exactly is not working in the Reminders app? Are you unable to open the app? If you haven't tried yet, we suggest to follow these steps when an app is not functioning properly:
If an app on your iPhone or iPad doesn't work as expected, try this.
1. Close and reopen the app
Force the app to close. Then open the app to see if it works as expected.
2. Restart your device
Restart your iPhone or restart your iPad. Then open the app to see if it works as expected.
3. Check for updates
To see if updates are available for the app, open the App Store, tap your profile icon, then scroll down to see if updates are available. If updates aren't available for the app, update the software on your iPhone or iPad.
4. Delete the app, then redownload it
Delete the app. When you do this, you might lose data that was stored in the app. Then redownload the app. Then check to see if the problem with the app is fixed.
These steps can help and is outlined in this article: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support
If that doesn't help, please provide the community additional details of what experiencing with Reminders and what steps you've performed. You mentioned attempting everything and it would help to know what those steps were to provide you the best support.
Kind regards.