Click onto the objective and scroll to the bottom of the objective pop-up. Add your final rating and select the tick box beneath to submit your final rating (depending on the account configuration you may have the option to add final comments).
When these are submitted to an objective, they 'lock' the objective and no further updates can be made. Make sure that you only submit these when you have completely finished working on an objective.
Note: The objective must be confirmed before your can add and submit a final rating within an objective.