Hello Sheila. If you find that your Outlook To-Do List is empty, the usual culprit is a sync issue or accidental deletion. Fortunately, your tasks should be stored in Microsoft Exchange Online so it is likely that your tasks can still be recovered even if they do not appear in the To-Do app.
To recover your tasks, open the Outlook desktop application and click Ctrl + 6 to use the Folder List view. Now, click the arrow to expand your Deleted Items folder. Scroll through the deleted items for folders or deleted tasks. If you find the task folder, right-click it and select Move Folder, then select your Tasks folder to recover your To-Do List. If your work in Outlook Web, you may be able to use the Recover Deleted Items option from the Deleted Items section.
Hope this helps.
Best regards,