I think you might be able to get closer by doing the following:
Under “función”, for the “Monto” row, set the value to “Suma”
Under “Grupo” for the “Asignado a” row, check the checkbox
Under “Grupo” for the “Monto” row, uncheck the checkbox
The above changes should Group the report by User & total the Amount of each item per user
If you make the above changes, how does the report look?
Is it closer to what you’re looking to achieve?