Edit opens the same window as Add plan, titled Edit plan: an older plan that also has a Why or Notes shows them inside the Description as paragraphs starting with Why: and Notes:, and saving puts each back in its place, while Save without changes closes the window and writes nothing. Remove asks to confirm: agents no longer receive the item, and its history stays in the project journal.
If the work was done, do not remove it: the agent that finishes it marks it Completed, so it stays as history, and the app has no status to change. Editing keeps the state, priority, affected modules, paths and dependencies the plan already has, which the app neither shows nor sends, a plan without a category or without Applies to (shown as Not set) can be given one, every edit goes through the same AI check as a new item, and every change, removals included, is recorded in the project journal with who made it.
If someone else changed the project while you were editing, nothing is saved: the page refreshes and tells you, so you can check the item and try again. Who can change Planning is explained in Who can change the Planning of a project?.