I submitted the vat then i needed to make correction on vat but it's affect the bank account ( the bank account decreases ) ?

Hello, maram-sahseh-co. 

In QuickBooks, we can either cancel or delete the VAT that has been filed. Though, this option is currently unavailable in QuickBooks Online. 

Undoing the VAT filling needs to be done by contacting our support team. They are the ones who can create a VAT unfiling request to successfully delete the VAT form. Before doing so, please prepare the following information:

1. QuickBooks Online Company ID. You can get your company ID by clicking the Gear icon and selecting Account and Settings. Then, proceed to the Billing and Subscription tab and look for the ID in the upper part of the screen. 
2. Which tax filing period do you want to unfile.

To contact them, you can log in to your QBO account. Then, follow these steps:

1. Go to the Help icon.
2. Type in Talk to a human and press Enter.
3. Select or type Contact Support.

You'll want to check this article for more details about managing VAT returns: Tax for QuickBooks Online. It contains topics about filing and paying tax, and applying sales tax to transactions. 

You can always get back here in the Community if you need further help or any clarification about the VAT process in QuickBooks. Take care always.