Workflow groups control the composition of workflow group members and require minimally 3 user roles : 

1. Requestor, 2. Approver and 3. Recruiter. Proxies are optional and are also managed within Workflow Groups

1. Click on the Building icon > Business Entity > Manage Setting > Workflow > Workflow Groups 

2. Click Manage Members 

3. Click Save to commit the changes made to the workflow group