If you are needing to enter a date that a division of a resource was worked on or completed (that hasn’t been marked as completed) – it is easy.
Beside the Today box, where you would mark it off for today, there is a little triangle to open up other dates it was worked on. You will see the previous week’s worth of dates, and you can mark it off there. If it is further back, there is also a little calendar button which opens up a calendar, and you pick a date to add to the list – then you can mark it off.
If you need to change something that has been marked off as complete – if it was the previously done division, you can click on ‘edit assignment’ where it shows the previous assignment. That will open up, and you can edit that one.
If you have done a few assignments after the one you want to change – you can edit the previous one, and clear all the worked on information – refresh the page, and repeat until you get to the one you want to fix – then reenter the information on all the other ones. (Usually not worth the effort…)
If you have finished the resource entirely…. then no, you can’t edit it. (If it helps, you can reschedule the resource – but it won’t remove anything already saved as done…)