[Lizard]

It depends on how the task dates were assigned. Changing the start date for the first task will update all the others, unless their dates were all explicitly assigned in the original template. (Select the earliest task and open the Task: Information inspector to find a convenient place to change its start date.)

Changing the project start date (in the Project: Information inspector) to today and then back to 'undetermined start date' might also push everything back to the beginning.

If neither of those work, please email our Support Ninjas (omniplan@omnigroup.com) so that someone can work directly with you to solve this problem.