Hi there, SunflowerSpaCorp. 

The option to convert transfer to expense isn't possible. However, if you have incorrectly categorized your transactions,  you can undo the transfer from the Categorized tab. Then, it will return to the For Review tab. From there, you can match it to an expense. 

Here's how:

1. Go to Banking from the left menu and click the Banking tab.
2. Choose the tile for the bank or credit card account you downloaded the transaction.
3. From the Categorized tab, find the transaction.
4. Click Undo from the Action column.

I've added a screenshot for your reference:

You may add the transaction that wasn't added in your QuickBooks you may then reconcile your account flawlessly:

• Categorize and match online bank transactions in QuickBooks Online.
• Reconcile an account in QuickBooks Online.

Please know that I'm just a reply away if you need any further assistance managing your bank transactions. Have a good one.