It looks like you’re talking about two different situations. Let me see if I can address both.
Situation 1: Editing recorded work. The Organizer doesn’t currently have a way to edit recorded work. We know this is a necessary feature and we are working on ideas for building it.
Situation 2: Recording work you missed. If you forget to record something, even if it’s not scheduled, it’s easy to backdate an assignment. First, make sure the resource is scheduled on your Daily Plan. If you only need to mark off one assignment, schedule just that one division. Next, find the resource on the Daily Plan and click the triangle next to the checkbox. That opens up a “drawer” with more checkboxes, plus a calendar that you can use to pick any previous date and mark it off.