No, you're not able to change your payment date in Turbo Tax once you've filed your return and it has been accepted but you can cancel it and then make other payment arrangements with the IRS. 

Yes, you can cancel the Federal Tax direct debit payment up to 48 hours (midnight, Eastern time) before the date you designated the funds to be debited. To cancel your direct debit transaction, call (888) 353-4537.But please wait 7-10 days after your return was accepted before calling.

• See Pay Taxes by Electronic Funds Withdrawal.

State : For your State direct debit payment you would need to contact your State directly to see if you can change the date or cancel the transaction. Each state is different you can find the contact information for your State by using this link to find the contact information for your State: How do I contact my state Department of Revenue?

Source: PaulaM

I called the IRS to attempt to cancel, but they said they cannot find my info.  I set the date to withdraw as 4/15, but I want to change  the withdrawal date to 7/15, the new deadline.

If you filed recently, the return has not been processed yet from their server.