Please select Employee  from the navbar menu
TimeOff.Management header
Then you will see a list of all employees.
Press on the name of employee you want to adjust allowance for.
Choose Absences from the menu.
Employee details page with arrow pointing to Absences tab
Once there, you can simply override department allowance in Nominal allowance field with individual allowance for employee.
Employee nominal allowance field screeshot
To learn how to set up allowances for different leave types please read article Leave types.