This assumes you have created a static inventory in Tower and have also appended one or more managed hosts to the inventory.

1. In the left panel of Ansible Tower, select Inventories.
2. Select the inventory you want to remove managed hosts from.
3. Select the Hosts button.
4. Select the trash icon for the managed host you want to remove from inventory.
5. When prompted "are you sure", select Delete.

In this example, server1.example.com will be removed from foo inventory.