Hi there, averyl.
For the multiple tax payable accounts created by the previous bookkeeper, you can inactivate them in QuickBooks Online. This way, you can only retain the Sales Tax Payable account you need when creating a transaction.
But first, let's open per invoice transaction to see if the correct sales tax code was applied. If not, then manually change to the correct one.
Once done, you can follow the steps below on how to inactivate the Sales Tax Payable account:
Then, repeat the steps above to inactive other accounts.
For more details about deleting an account, you can refer to this article: How to delete an account or restore a deleted account.
I've found a helpful article for more details about managing sales tax in your Online account: Sales tax in QuickBooks Online.
Feel free to reply to this thread if you have more questions in sales tax.