We are unable to change the earlier passed entry. If we try to change the entry we are getting an error pop up as cannot assign tax code on tax account.

I'm happy to see you here in the Community, @indiatax.

It's my priority to ensure that you'll be able to assign tax codes on your tax forms in QuickBooks Online.

If you're referring to modifying a filed tax form in QuickBooks Online, you'll need to reach out to our Customer Care Team. This way, they'll be able to unfile the form, so you can make necessary changes. Know that being able to directly edit the submitted tax form isn't available.

Before contacting them, please prepare your QuickBooks Online Company ID and which tax filing period you wish to edit.

To reach them:

1. Click on Help at the top menu bar.
2. Select on the Contact Us button.
3. Enter a brief description of the issue in the What can we help you with? box.
4. Press on Let's talk.
5. Select on Get a callback.
6. Key in your contact details, then tap on Confirm my call.

To learn more about the unfiling process, kindly refer to this article: How to unfile VAT/GST.

I'm also adding here some articles that can help you in filing and paying taxes in QucikBooks Online:

• File your tax return and record tax payment in QuickBooks Online
• Manage tax payments in QuickBooks Online

If you're referring to something else, please let me know. I want to ensure you're taken care of. Just leave a reply below. Keep safe!