You can select direct debit https://accountants.intuit.com/support/en-us/help-article/federal-taxes/common-questions-e-filing-in... just like on an original return.

You can do both. If you choose to pay online, make sure to update that - under the current amended return – Payments & Credits, enter your ACH/EFT payment amount and payment date. The software cover page will refresh and indicate that no balance nor payment action is required.

If you decide to mail a check along with the return, please note that the mailing address will be different (usually the software will provide this information), as the processing office will vary for amended returns with and without payment.