Running 'advancement assignment' will align the past assignments with the times achieved by the resources (the actual work) until the 'progress date'. So you can easily take into account the work done to adjust future assignments.
To access it you have to go to 'Project> Resource> Load'
As shown in the view below, the blue vertical line represents the date of progression and the orange vertical line represents the current date.
Click on 'Work and actual' to see in each box : below the work done and at the top the planned work. We can see in the example that work was done for 'M1' and 'T2' (Monday 1st and Tuesday 2nd of July). Nothing has been done on 'W3', 'T4' and 'F5' (Wednesday, Thursday and Friday), the lower part is empty.
The column 'Past assignment' indicates that 3 days in the past have not been performed. As the week is over and the actual time has been entered, it means that planned work could not be done. It must be rescheduled in the future so that this load appears in the resource planning and the task schedule is updated (indeed, this can affect other tasks, for example when there are dependencies between several tasks). For this, we will press 'Progress assignment'. This action can only be performed if the work have been allocated in 'man.day' and not in 'percentage' of the duration. If this is the case, the tool will propose you to change the task allocation into 'man.day' before performing the progress.
As you can see the unperformed work in the past has been removed and transferred to the Delta ETC column (Delta of estimate to completion : This column indicates the difference between what has been allocated and the actual + ETC). If you think the result is what you expect, you can press 'Commit'.
To reallocate this remaining workload, all you need to do at a later date is to enter the new assignment. In the example we entered 1 day for Monday July 15th, which meant that the Delta ETC (Delta of estimate to be done) automatically decremented. The same must be done for the remaining two days in the Delta ETC column so that its value is equal to 0.
You have progressed your assignments successfully. Your planning is now up to date. Congratulation.