We don't have a proper guide, I'm afraid, but I'll try to explain the steps:
In the Flic app:
Connect the Harmony Hub provider (Providers are found in the top right menu).
Go back to your list of Flics (or Tasks) and tap one of them to edit it.
Choose a trigger (like Click).
In the list of actions, look up Harmony Hub and tap it.
Select the "Activity" you want to use in the list, like "Turn on TV".
Press "Add".
Now you should be able to turn on your TV by pressing your Flic!
Let me know if this helped!
If you have the Harmony app, you can verify that the Activity is working by tapping the on/off toggle. If it works in the Harmony app, if should work in the Flic app.