If you have filed already then you might be too late to make changes because cancellation requests must be received no later than 11:59 p.m. ET two business days prior to the scheduled payment date.
Usually you can call IRS e-file Payment Services 24/7 at 1-888-353-4537 to inquire about or cancel your payment (wait 7 to 10 days after your return was accepted before calling) and then pay your taxes online but since your payment date is already tomorrow you will not be able to cancel it.
If you haven't filed then select that you will pay with a check and then you can pay your taxes online at the IRS site.