If you have already subscribed to HER Premium but the features are not working please try the following:
1. Close the app and then restart it
2. When you tap on the icons in the top left or right hand corners, does a premium purchase appear? Alternatively, when you go into settings are your premium features available?

Restore purchase is like a reset button for premium. It won't charge you again, just sometimes needs another push to start.
You can restore your purchase by:

Apple Device:
Going to My Profile
Then tap on Settings in the top, left hand corner 
Scroll down below the list of Premium features and select "Restore Purchase"
Then follow the steps from there

If you are using an Android device:
Select any of the HER Premium features icons or Upgrade Access in settings
Select Restore Subscription