To file a zero income tax return online, visit the official website of the Income Tax Department of India at incometaxindia.gov.in and select the "e-File" option from the "Services" tab. From there, select the "Income Tax Return" option and enter your PAN number, assessment year, and other relevant details. In the "Income Details" section, select the option for "Income Tax Return - 0" to file a zero income tax return.