iPhone Data Recovery can easily solve this problem for you. You can use this program to scan your phone and then find the deleted calendars for you. You can preview them before recovering. Learn how to recover deleted calendars from iPhone
. Besides calendars, you can also recover messages, photos, videos, contacts, call history, notes, reminders, voice memos, voicemail, safari bookmarks, Whatsapp messages and other deleted data from your iPhone 7.