You can manage who has access to a workflow by making it visible only to certain individuals or permission levels.
Check out this clip from Planning Center University.
From the workflow, choose who to give access to the workflow based on their permission level, or you can choose a specific person.
You can only share workflows with users who have permissions of at least Viewer.
Choose the type of access you want them to have.
When someone doesn't have access to a workflow, they won't see it in the list of workflows or see any of the workflow's cards from a profile page. Unless you've told them about it, they won't even know the workflow exists.
From the Workflow, click the x to remove a permission level or person's access to the workflow.