The progress of each objective is based on the progress of its key results, thus you cannot update the value of the objective’s progress yourself.
What you can do, is posting regular updates on how the overall work on the objective is going in relation to its status.
Go to the objective’s page.
Click on the “Post an update button”. add screenshot
Choose the objective’s status. add screenshot
Write a summary of the progress of the objective. You can treat this description as a message for everyone interested in this objective that will give them a sense of the current state of matters. add screenshot