Adding edits from AAP-38722 (#2864) (#2866)

Author: g-murray

downstream/modules/platform/proc-post-migration-cleanup.adoc

@@ -4,7 +4,9 @@
 
 [role=_abstract]
 
-After your data migration is complete, you must delete any Instance Groups that are no longer required.
+After data migration, delete unnecessary instance groups and unlink the `old database configuration secret` from the {ControllerName} resource definition.
+
+== Deleting Instance Groups post migration
 
 .Procedure
 . Log in to {PlatformName} as the administrator with the password you created during migration.
@@ -17,3 +19,14 @@ Note: If you did not create an administrator password during migration, one was
 . Select {MenuInfrastructureInstanceGroups}.
 . Select all Instance Groups except controlplane and default.
 . Click btn:[Delete].
+
+== Unlinking the old database configuration secret post migration 
+
+. Log in to *{OCP}*.
+. Navigate to menu:Operators[Installed Operators].
+. Select the {OperatorPlatformNameShort} installed on your project namespace.
+. Select the *Automation Controller* tab.
+. Click your *AutomationController* object. You can then view the object through the *Form view* or *YAML view*. The following inputs are available through the *YAML view*.
+. Locate the `old_postgres_configuration_secret` item within the spec section of the YAML contents.
+. Delete the line that contains this item.
+. Click btn:[Save].