Let's understand how rewards work.
As soon as you click "Rewards" link on your left-sidebar, you will reach a screen similar to the one below:
You can see the name, Points you need to claim the reward and other details.
Note that you may or may not see the rewards and it will depend on the project you are promoting.
If you are eligible and you have enough points, Click on "Claim" button to request rewards in exchange of your points.
If your work meets the guidelines, the ambassador program manager will Verify your work and you will receive the points for completing the Task.
Once your rewards are accepted by the team, you will be able to see them in your profile and also in "Accepted" Section.
This is it.
You can ask in the Community or talk to your project manager if you have any further question