VAT rate’s Purchase account is wrongly mapped and I can’t change it in Edit rate screen. Input VAT missing from VAT return. Need help fixing this.

QuickBooks prevents editing default VAT rates and limits modifications to custom ones. Additionally, please note that any rate updates apply only to future transactions.

To resolve this, you must create a new tax rate with the correct settings, deactivate the old one, and perform a prior-period VAT adjustment.

Here's how to make the old rate inactive:

1. Go to All apps, select Tax, then click Overview.
2. Select Edit VAT, then click Edit rates.
3. Find the old or incorrectly mapped VAT rate, click the dropdown in the Action column, and select Make inactive.

To make a tax adjustment, please refer to Step 2 in this article: Create or delete a tax adjustment in QuickBooks Online.

Let us know if you need anything else.