An AI's Head Transform is used to provide an accurate position of where their line of sight and field of view is based off of.
The first time you are setting up an AI's Detection Component, you will receive a warning message about an AI needing a Head Transform.
You can assign a Head Transform by opening up the Detection Settings foldout and finding the Head Transform slot. Pressing the Auto Find Head Transform will attempt to automatically find it. However, this does not always work. If the Head Transform slot is still empty after pressing the Auto Find Head Transform button, you will need to assign it manually. If the Auto Find Head Transform works successfully, ensure the right transform was applied.