Super Admins and custom role owners with company-wide Succession Planning admin permissions have the ability to delete plans.
Delete a Succession Plan
Navigate to Admin > Performance > Succession Plans.
Click on the name of the user whose plan you'd like to delete.
Select the ellipsis (...) on the top righthand corner > Delete.
A pop-up will appear where you can check the box confirming the action of deleting the plan. After you have clicked the box, select the option to Delete.