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Initially approvals are inherited form its parent folder or its root folder. To change that enable the Override Approvals toggle.
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Click the Create ->Approval→ Approval button to create a new approval, or to edit an existing approval, select the approval and click the Edit button.
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Select the Environment, Workflow Type and click on next button to select Change Management Instance and Approval groups.
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Can select one or more Groups to the right who must approve deployment requests to that environment. Click the Save button to save the changes.
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