The documentation here: http://manageiq.org/docs/reference/latest/doc-Installing_on_Red_Hat_Enterprise_Linux_OpenStack_Platform/miq/#configuring-an-internal-database
says that you can create a key or fetch a key when entering the menu for configuring the database.
Select 5) Configure Database from the menu.
You are prompted to create or fetch an encryption key.
If this is the first ManageIQ appliance, choose 1) Create key.
If this is not the first ManageIQ appliance, choose 2) Fetch key from remote machine to fetch the key from the first appliance. For worker and multi-region setups, use this option to copy key from another appliance.
All ManageIQ appliances in a multi-region deployment must use the same key.
Choose 1) Create Internal Database for the database location.
This option does not exist.