Access Subscriptions from the switcher. You will be redirected to the My Subscriptions window.
Select Manage Trial from the My Subscriptions window.
You can access a summary of your subscriptions, including the add-ons you are eligible to try out.
On clicking Manage Trial, you can access Change plan, Buy Plan and other streams that let you modify or activate your subscriptions. If Add ons are available for your product, you can try those out too. 
For more queries, write to [email protected].