Hello there, namhla,

In QuickBooks Online (QBO,) account numbers are manually entered. Let me show you how it's done.

You need to enable the option and manually allocate for each account in your Chart of Accounts by following the steps below.

To enable, here's how:

1. Go to the Gear icon, then choose Account and Settings.
2. Select the Advanced tab.
3. In the Chart of Accounts section, click the Edit (pencil) icon.
4. Check Enable account numbers and Show account numbers. (Please see screenshot below).
5. Click Save, then Done.

Once done, you're now ready to allocate one to your accounts. Here's how:

1. Go to the Gear icon, then choose Chart of Accounts.
2. Above the Action column, select the Edit (pencil) icon. 
3. Enter the account numbers in the Number column. (Please see attached file below).
4. Click Save once done.

That'll get you going, namhla. For the detailed steps, you can refer to this article: How to Enable and Use Account Numbers.

Should you have other questions about QuickBooks features, let me know by leaving a comment. I'm just around if you need help.