You may have 2 following options:

1. Use a 3rd party backup restore app

https://partnerwithus.rewind.com/quickbooks

2. Convert your data to a QB Desktop file format. You can use the trial version to open the file later.

The security of your data is our priority. That's why we’ve invested a great deal of thought and resources into ensuring a completely reliable system, Novoto.

In QuickBooks Online (QBO) Advanced, you can save online backups of your accounting data. Backups save everything on your chart of accounts. You can schedule automatic backups, do one-time manual backups, and even save copies to DropBox or Google Drive. To learn more about this one, check out this article: Back up and restore your QuickBooks Online Advanced Company.

For other versions of QuickBooks Online including the Plus version, you don't need to worry about saving your QuickBooks data on a flash drive. QBO automatically backs your data up with the same level of security used by banks and financial institutions. We update your records with every change, however, we can't restore your file to a previous point in time compared with the QBO Advanced version. This is how we keep your data safe and secure: 

• Whenever there are changes to your company file, your data is saved to two hard drives.
• We periodically copy all data to a third-party hard drive. This means your data is protected in case something happens to the first two hard drives.
• Automatic backups are performed every night.

In your case, you'll need to manually export data out of QBO and save copies onto the computer's hard drive. Many forms, lists, and reports have a download button. And, I'm glad to show you the steps.

1. Go to the Gear icon from the toolbar.
2. Under Tools, select Export Data.
3. On the Reports tab, set the date range.
4. Add or remove items from the Reports and Lists tabs by toggling the slider.
5. Press Export to Excel.

You'll be prompted with confirmation that the data has been exported. You can check out this article for additional reference: Export reports, lists, and other data from QuickBooks Online. It includes moving non-posting transactions and attachments.

Looking for a continuous backup of your data? Several apps are already integrated with QBO. You can find one through our site: QuickBooks App.

I'm happy to help! Give me a shout if you need anything else by commenting below. I'm always around to help back up your QuickBooks data. Take care always.