How to fill “days left” for a user?

Hello,
The margin is calculated regard to the cost or day validated and the cost or day reassessed (if I well understood).
So I at the beginning of a project you have to validated a load in days.
For instance:
-if I have a project validated with 100 days at the starting,
- at the middle of the project I have spent 60 days (instead of 50),
- I make a reassessment because the project shift, and the remaining load is not 40 days but now 50 days,
- So my new margin in days is now -10 days.
When you are manager you can access to the menu “work/activities/assignment/left” and modify “left work” (which is by default equal to 40 days regard to my example) and set it at 50 days to put in evidence the shift in load of 10 days.
Is it the only way to put in evidence the shift? And when you are a simple user how can you modify the “left work” as users have not access to the menu “work/activities/assignment/left”.
Thank by advance for any precision.
Eric

Simple user can use "Real work allocation" screen.

The column "Left" allows to change the left work for each task.

Ok thank you for your reply