If you filed for an extension, then you already filed Form 4868 or the equivalent. You do not need to file it a second time.
Perhaps I misunderstood your issue. You do NOT have to send money when you file Form 4868. Suppose, for example, that you are due a refund, but you just haven't had the time to complete the tax form timely. You can file a Form 4868 to request an extension of time to file. On Form 4868, just indicate the amount you are paying with the extension form as $0. Indeed, the form could list your estimated tax total as well as how much you already paid (e. g., through withholding), and if the amount paid exceeds the amount due, you file the form without sending any payment.
@SLR-DI I did end up owing taxes last year but I paid an estimated amount when I filed for the extension. Now that the extension is over I’m getting ready to file federal taxes and TurboTax is showing me entries that are missing. One of which is the “Amount you are paying with your extension”. Now that I’m finished, the amount I owe is still less than what I paid so I’m assuming I just put $0 since I’m not paying any more than I already paid.