How do I clear out old sales tax liabilities paid incorrectly.

Hello there, @Rhiannonrwc. 

I want to help ensure that the check will be posted on the liabilty account. Since the transactions is way back 2014, suppose the books are already closed. 

At this point, you can create a journal entry to correct this. It helps you move money between two different accounts. Here's how: 

1. Go to the Company menu, then select Make General Journal Entries.
2. Enter all necessary details to create your journal entry. Make sure your debits equal your credits when you’re done.
3. Click Save & Close.

To make sure your books are accurate, I recommend consulting your accountant for guidance. 

For future reference, check out this article to help you learn more about processing sales tax adjustment in QuickBooks.

Get back to me if you need additional assistance in correcting your transactions in QuickBooks. Take care!

@Rhiannonrwc 

If there's still a balance in the sales tax payable liability account, you will need to create a journal entry: debit sales tax liability, credit sales tax expense.  Alternatively, you could credit an income account since a negative expense looks odd on a P&L and the net effect is the same.  This will remove the liability and correct the sales tax expense that was taken in error for the past 8 years.  Depending on the amount of sales tax collected and recorded as an expense, this could create a significant increase in income, and tax liability, for your client.