A supplier's bill was entered as a billable expense. This appears as a creditor on the balance sheet. Next year its discovered that it is an error. How to correct?

I'm not sure I understand

marking an expense as billable does not affect anything, it is a tag telling QB that when you invoice the customer you will want to charge him for this expense and QB provides a way to just click and add it to the customer invoice.

The bill, if not paid, will change the balance sheet A/P account, but that is normal.

Could you include a screen shot of the bill, and the balance sheet where it is showing?