Final answer:
The Blackboard app is typically available for free on smartphone app stores, but Diamond must have the necessary login credentials from her educational institution to use it.
Step-by-step explanation:
Typically, the Blackboard app is available to download at no additional cost for users with an account associated with their educational institution. To add the Blackboard app to her smartphone, Diamond should simply go to her device's app store, such as Play Store for Android or Apple App Store for iOS, search for the Blackboard app, and proceed to download and install it. Keep in mind that while the app itself may be free, Diamond might still need to use login credentials provided by her school or college to access the full functionality of the Blackboard learning platform.