On Form 740, below the Filing Status, there is a checkbox to indicate the return is amended.

From Kentucky Government instructions:

AMENDED RETURNS-Beginning with tax year 2017, you may file an amended return by checking the "amended" box on the first page of Form 740.  You will still need to provide a copy of federal Form 1040-X and any supporting schedules.  Continue to file Form 740-X to amend returns prior to 2017.

See the "Reminders" section at https://revenue.ky.gov/Forms/740%20Packet.pdf