Why can't I change my event date?
If you've already sold tickets and been paid out for a Splash event, you will not be able to change the date and time for that page.
If the date and time is locked in the Settings tab, you can either (1) duplicate your old page or (2) create a brand new event page.
Check out: Can I create a recurring event?
Using one page per event is crucial to the operations of your ticket sales and event payouts. Make your accountants' lives easier by keep accurate accounting information organized per event.