Easiest way is to close the account, if it hasn't already been frozen once Social Security notified the bank.  I had a client who had set up a Sept 15, 2022 payment (through another preparer) --  it didn't clear.  

If you look at the 8879 that they signed for 2022, it has a phone number.  I think the estimated payments can be cancelled by calling that phone number.

You mean, they would have signed it for 2023. 

Assuming your client does not have a surviving spouse, the executor or administrator of your client's estate will need to file a Form 56 Notice Concerning Fiduciary Relationship with the IRS to notify the IRS of the existence of a fiduciary responsibility, if they have not done so already.

The executor or administrator would then have to contact the IRS' e-file Payment Services at 888-353-4537. Or, they can give you a power of attorney (Form 2848) to call on their behalf.

Pay Taxes by Electronic Funds Withdrawal | Internal Revenue Service (irs.gov)