...
This option is only available when there is no space approvals enabled.
Adding an approval
Go to a page and
choosechoose the ellipsis menu icon
to open Page Tools
Select Add Approval from the down menu:
...
Appears for pages and blog posts:
Only when space approvals is disabled
Only for users who can edit or admin the content
The Approval workflow is added to the individual page or blog post. Once added you can interact with the approval workflow via the Approval Status Bar.
The initial state of the page or blog post is the 
Review state.
...