I already paid my taxes with a credit card, need to change payment method on turbo tax 1040 form

Did you already file?  Then you can't change it.  If you have not filed then when you go through the File tab pick that you will mail a check so your bank info doesn't get transmitted.  

Or did you make a payment with an extension?

To enter the amount you paid with an extension (including state extension)  go to

Federal Taxes (or Personal for desktop H&B version)

Deductions and Credits

Then scroll way down to Estimates and Other Taxes Paid

Other Income Taxes - Click the Start or Update button

Next page second section Payments with Extension

Either Visit All or Click Start or Update by the extension you paid