There is not a single “right” way to make a Fourth Step Inventory, but Al-Anon is full of great literature resources with suggestions and guides for members and groups.
For Individuals:
Blueprint for Progress: 4th Step Inventory
Reaching for Personal Freedom – Living the Legacies
Paths to Recovery: Al-Anon’s Steps, Traditions, and Concepts
For Groups:
Taking a Group Inventory (G-8a)
Taking a Group Inventory – Methods and Suggestions (G-8b)
The Al-Anon World Service Office blog posted an article from the February 2024 edition of The Forum highlighting the benefits of taking an inventory.