Add missing step to the "How to add non-ECS fields to Attack Discovery" procedure (elastic#3524)

Closes elastic#3504.

Author: alaudazzi

solutions/security/ai/attack-discovery.md

@@ -54,6 +54,7 @@ Attack Discovery is designed for use with alerts based on data that complies wit
 1.  Select an alert with some of the non-ECS fields you want to analyze, and go to its details flyout. From here, use the **Ask AI Assistant** button to open AI Assistant.
 2.  At the bottom of the chat window, the alert's information appears. Click **Edit** to open the anonymization window to this alert's fields.
 3.  Search for and select the non-ECS fields you want Attack Discovery to analyze. Set them to **Allowed**.
+4.  Check the `Update presets` box to add the allowed fields to the space's default anonymization settings.
 
 The selected fields can now be analyzed the next time you run Attack Discovery.
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