Remove the date. The defaults to filing date, if after the original due date.

I am unsure, but I don't think you can set up direct debit with the 1040X. The Letter (US Standard) should have the answer to this. If there is a balance due, then there is likely interest also due. I would direct the client to make the payment via https://www.irs.gov/payments/direct-pay

From the instructions:

Line 20—Amount You Owe
See the “Amount you owe” section in your income tax return
instructions or go to IRS.gov/Payments for payment options.