Explanation
The client has two objectives:
1. Move website users to the mobile app.
2. Create new mobile app downloads from new users.
For the first objective, you want to create a custom audience based on your client's customer base in order to move website users to install the mobile app.
For the second objective, you want to reach out to people who have interacted with the brand before and new potential users. In this case, your best option is to market to fans who have interacted in the past 90 days and also a new audience based on the current customer base.