You can resume a Test Cycle that is in "ABORTED" and "COMPLETED" status.
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Launch a Test Plan issue
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Click the "Gear" icon from a Test Cycle in "ABORTED" for "COMPLETED" status
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Click "Resume" from "WORKFLOW"
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Once the Test Cycle has been resumed, its status will change to "ACTIVE"
[Screenshot - UG_TM02_Test_Cycle_Resume]