You can't, but you can select an existing report and use the Adjust/Edit to change the the time or quantity value as required. You can of course also first cancel the existing reported value and then report again. 

The business goal is that he wants to update the value of work on the operation.
Example
I have registered work on the operation 4h x 50 Euro (cost of a production slot)

In this particular order I wanted to get the cost of 150Euro.
I planned to add a line -1h x 50 Euro. And mark this line that this is a change and not the actual registration time

How to achieve such an effect?

You can find the report for the 4 hours and use the Edit Operation Result to change from 4 to 3 h

Thank you for your reply. I understand that we don’t have the ability to change the value.

Topic to be closed :)