Hello there. Welcome to the Community space. I understand the importance of exporting your chart of accounts which includes your account number.

I'd like to lay down the steps and details with screenshots that can help for your visual reference. The account numbers feature is off by default. Here’s how to turn it on:

1. Go to Settings gear icon and select Account and Settings.
2. Select the Advanced tab.
3. Click the Pencil icon in the Chart of Accounts section.
4. Turn on Enable account numbers. If you want account numbers to show in reports and transactions, check the box to Show account numbers.
5. Click Save to confirm.

With this, follow these steps to export your Chart of Accounts that include an Account number:

1. Go to the Report and search the Account list.
2. Select Switch to classic view. 
3. Click the gear icon and make sure to check the box in the Account #, then Save customization.
4. In the upper right, find and click the drop-down arrow labeled Export.

In addition, you can visit this link to learn how to get started with Memorizing Reports in QuickBooks Online: Memorize reports in QuickBooks Online.

If you have more questions about customizing your reports or any QuickBooks-related concerns. Feel free to comment down below. Stay safe.