Let me share some information about how to update your QuickBooks for Mac, Mary.

Make sure that your QBDT is in an Applications folder, simply drag the QuickBooks icon to the Applications folder, if the issue persists, you need to clean install. Here's how to manually update your QBDT account:

1. Uninstall QuickBooks for Mac, and close QuickBooks.
2. Then from the Finder menu, select Go Applications.
3. After dragging the QuickBooks icon to the Trash.
4. Reinstall the latest version. Go to QuickBooks Downloads & Updates.
5. Make sure to select the correct country, product, and version.
6. Select Search. Then click  Download to download the installer file.
7. Double-click the .dmg file. Drag the QuickBooks icon to the Applications folder to install.
8. Restore your company file in QuickBooks.
    

To learn how to keep QuickBooks for Mac up-to-date so you always have the latest features and fixes, check this article for more details: Update QuickBooks for Mac to the latest release.

Also, I'd recommend creating a backup of your company file for future data restoration purposes. You can check out this article to guide you through the steps: Back up your QuickBooks Desktop for Mac company file.

Let me know if you have any additional concerns or questions regarding the QBDT update for Mac. I'm here to assist you.