Enable or disable the Calendar tab in Salesforce Lightning Experience

IMPORTANT: Our first step is to disable the Enhanced Profile User Interface, since we can only see the Calendar tab on the profile if the said feature is disabled. 

 
 Steps to disable the Enhanced Profile User Interface

1. From Setup, enter User Management Settings in the Quick Find box.
2. Select User Management Settings.
3. On the User Management Settings page, disable the Enhanced Profile User Interface.

Once the Enhanced Profile User Interface is disabled, we can now proceed to enabling or disabling the Calendar tab on the specific profiles by following the steps below:

1. From Setup, enter Profiles in the Quick Find box.
2. Select Profiles.
3. Edit the profile you want to adjust.
4. Scroll down to the Tab Setting section where we can see the Calendar setting.
5. We may then set the Calendar Tab to either 'Default On' or 'Tab Hidden' as the value, then click Save.