How should an ATM withdrawal be reconciled if it isn't showing up as a transaction?

Hello there, @ms773-aol-com.

Thanks for asking the Community about your reconciliation concerns.  

Any transaction that isn't in QuickBooks needs to be added manually so you can reconcile them with your actual bank statements. 

Here's how to do it directly to your registers:

1. Go to Settings menu, then select Chart of accounts.
2. Find the account register you want the transaction to appear.
3. Click View register from the Actions column, then click the Add journal entry, Add check, or Add deposit ▼ dropdown menu.
4. Select the type of transaction you want to add and enter all other details in the fields to complete the transaction.
5. Select Save.

For additional reference, visit this article: Manually add transactions to account registers in QuickBooks Online.

Check out this article too for more guidance in reconciling an account in QuickBooks Online.

Get back to me here if you have more questions or if you need more assistance in reconciling and managing your transactions. Take care!