To export a calendar from Yahoo, log into your Yahoo calendar, navigate to the calendar you want to export, click the down arrow next to the calendar name, select "Export", and then save the downloaded calendar file to your computer; this file will usually be in iCal format.
Key steps:
Access your Yahoo calendar.
Select the specific calendar you want to export.
Click the down arrow or menu option next to the calendar name.
Choose "Export" from the menu.
Save the downloaded calendar file to your computer.