Note:Once deleted,you can not restore it.
■Fot those who have an account
Follow two steps to delete an account.
①Leave the calendar from "More" tab
②Tap four parallel horizontal lines on the upper left corner.
Tap profile section (your name and mail address) on the top of the page
Tap "Leave and delete account" on the bottom right corner
■Fot those who don't have an account
Leave the calendar from "More" tab
Uninstall an app