Hi there, @nonyanon.

You can prepare an Excel CSV for the missing entries from January to September 2020. Then, upload the file to QuickBooks Online (QBO). I'm here to guide you with detailed instructions.

First, get the transactions from your bank.

1. Sign in to your bank or credit card's website.
2. Follow your bank's instructions for how to download CSV files of your transactions to your computer. 
3. Check the date range for the download. It should be at least one day before the date of your oldest transaction.
4. Download your transactions. Save the file somewhere you can easily find it, like your computer's desktop.

After that, review the file format and size before uploading the transactions. If the file is too big, shorten the date range and download transactions in smaller batches.

And, here's how you can upload the file to QuickBooks.

1. Click on Transactions or Banking at the left pane, then go to the Banking page.
2. Select the blue tile for the account you want to upload the transactions into.
3. Tap on the Link account dropdown, then Upload from file.
4. Hit Browse, then select the file you downloaded from your bank. Then select Next.
5. In the QuickBooks account dropdown, select the account you want to upload the transactions into. Then select Next.
6. Follow the onscreen steps to match the columns on the file with the correct fields in QuickBooks. 
7. Click Next, then select the transactions you'd like to import.
8. Hit Next, then Yes.
9. When you're ready, select Let's go.

Once the transactions are available in QuickBooks, it's time to review and categorize them so you can proceed with your reconciliation.

Please feel free to get back to me here for any additional questions about your banking transactions. I always have your back. Thanks for dropping in, and cheers for more success!