Removing CalendarSync from a phone is as easy as setting it up!
Please follow these 3 steps
Open 'Settings' on your iPhone or iPad and tap on 'Mail, Contacts, Calendars'. ...
Scroll to 'Password & Accounts' and look for 'Subscribed Calendars' and tap on it.
Find the desired Getslick calendar you want to remove and click on it
At the bottom of the screen then tap on 'Delete Account'.