You can amend high level plan details via the ... More Options menu, from here you will see the option of Edit Plan.

From the Edit Plan modal window you have the ability to:

• Change the Group which the plan is aligned to
• Edit the name of the High Level Plan
• Add or amend the Associated to Event
• Update the Start Time of the Plan
• Amend the Duration of the Plan
• Configure the Late Duration
• Configure the Early Start and Late Start Tolerance
• Configure the Less and More Duration Tolerances
• Add or amend the description