If you created an event and you want to edit the dates revolved around it you'll have the opportunity to on the specific event management page to click on "dates" and update the following date, start time, end time and if you want to include shifts (Note: once you add shifts, the shifts will need to be created in a separate section after clicking Save and Continue, also take into consideration that you can have an event where people are registered to a single day event and if you decide to add shifts later you would need to move them into the specific shifts created otherwise they are orphaned).
Shifts: Once shifts are added you will see the following section "Shifts" available for you to import or add shifts individually (since the below example is for a single day event, the shifts each alone can be for different days, Note: when an event is recurring (ongoing) or is more than just a single day, a shift created for a recurrence will be limited to only the start and end time within the day of the recurrences:
Recurrence (ongoing): Once you decide to create an event with recurrences, when editing the event, you will see a section for dates. All the dates in the recurrence can be specifically updated or you can collectively update all of them or individually select a specific row/date to edit the "registrants", the number of spots or to delete them. Note: If you created a recurring event with shifts, "dates" is the area that defines the days in which people can register to, and "shifts" defines the times available.