I'm here to share some information that can help you correct the account of your billable expense to invoices, @TerriSR.

As mentioned above, linking an existing invoice and expense is not possible. You can open the billable expense you mentioned then update the account or category. Let’s ensure that the amount remains the same while doing this.

Since you mentioned that you already have added the billable expense to the invoice, you can click the billable expense then change the account. I’ll show you how:

1. Open the invoice in question.
2. Select the little chain icon.
3. Click Billable Expense then, Yes.
4. On the Billable Expense page, change the account to the correct one.
5. Hit Save.

 
I’ve included some snippets below as your reference:

If you opt to void or delete transactions in QuickBooks Online, you can check out this article. This will help you learn their differences including how it will affect your account balances.

Here's an article that'll guide you when receiving and recording invoice payments.

Post your concerns or click the reply button for any follow-up questions about adding billable expense to an invoice. I'm always here to help. Keep safe!