The Intrusion detection system notifications configured (AWS) test requires that a cloudwatch event rule exist to notify administrators of Guard Duty events. This must be set up for every region where a VPC exists by following the instructions linked here.
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If it does not make sense for Guard Duty to be enabled for the region flagged on the test page, you can deactivate monitoring for the region on the test page.

Removing the region from scope is another way to remediate a flagged part from that page, but only do this if there are no resources in that region that should be in scope.
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