You can edit the reference date of a started checklist to reschedule all its tasks. To do so :
Go to the template of the checklist to reschedule.
Locate the relevant checklist and click on the button with the three vertical points
Click on Reschedule Checklist
A window opens, enter the new reference date in the field
Click on Reschedule
Note that only tasks that are still open tasks will be rescheduled.