Glad to have you here in the Community today. I'm here to help share some information about recording sales receipts under the Undeposited Funds in QuickBooks Online.
To ensure we're on the same page, may I know why you are going to delete the sales receipts? If the amount has been deposited already in the Undeposited Funds, you'll have the option to delete it by clicking on the More option at the bottom of the transaction and select on delete.
However, if you wish to record the sales receipt under the Undeposited Funds, you may follow these steps:
Select the Plus icon (+) on the Toolbar.
Under Customers, choose Receive Payment.
Select the Customer name from the drop-down list.
Enter the date you were paid in the Payment date field.
Select one of the methods from the drop-down list in the Payment method field.
In the Reference Number field, enter the check number.
Select Undeposited funds from the Deposit To drop-down list.
Select Save and close.
Also, here are some great articles that you can check out about deleting sales transactions and how Undeposited Funds works in QuickBooks online for your reference: