Following are the Steps to Create Blackouts from EM Console:
1). Login to OEM 12c -> click Enterprise -> Monitoring -> Blackouts.
2). Click on Create.
3). Enter Name, Comments, Reason and Select the Targets and click Next.
4). Select Members Targets to Blackout and click Next
5). Select TimeZone, Duration and click Next.
6). Review the details given for Blackout and click Finish.
7). You can see the Blackout confirmation message as shown below:
8). Go to Targets and select the Blacked out component. in my case see the screenshot below: