OK. depending on which you want to use here are the directions:
#1 Restore Deleted iPhone 5S
Calendar from iTunes
First of all, make sure your lost calendar have been backed up on the iTunes, and do not sync your iPhone 5s with iTunes until get the files back.
First, plug your iPhone 5S into your Mac/PC via the USB cable. Launch iTunes and click “Summary” tab, then tap “Restore from Backup”. Not only can you recover calendar but other files as contacts, text messages, photos and more.
#2 Retrieve Calendar from iPhone 5S with iCloud
To retrieve calendar from an iCloud backup, you must erase the contents on your iPhone first by doing like this:
Setting> Reset> Erase All Contents and Setting
Then the iPhone will restart and run to the Setup Assistant tab, just select “Restore from iCloud” and sign in iCloud account.