The 540 Schedule X instructions give you some options for paying what you owe with an amended return.
"Line 7 – Amount You Owe
Pay online with Web Pay. Go to ftb.ca.gov/pay for more information.
You may also pay by credit card. Call 800.272.9829 or go to the ACI
Payments, Inc. (formerly Offical Payments) website at officialpayments.com
and use the jurisdiction code 1555. ACI Payments, Inc. charges a convenience
fee for this service.
Or, if you are not required to remit all your payments electronically, make
a check or money order payable to the “Franchise Tax Board” for the full
amount you owe. Write your SSN or ITIN and the taxable year you are
amending. "
If you are planning to mail a check, download payment voucher 3582 and follow the instructions on it.