In QuickBooks Online (QBO), once the VAT feature is turned on, there will be no option to turn this off. Since the entity or your client isn’t registered for VAT, let's choose Out of Scope of Tax or No VAT as the default tax rate selection. Theis used for non vat registered businesses. Choosing this option will not show any tax reports in your account.
To do it:
Go to the Gear icon.
Choose AccountsandSettings.
Click Advanced.
Go to Accounting.
Click the drop-down in Default tax rate selection and choose OutofScopeofTax (or No VAT.)
Hit Save. Then, Done.
You might want to visit the following link to become more familiar with the features and functions of QBO: