I am currently using SharePoint Online through Office 365 and recently obtained MS Flow in my suite of apps. We have an existing SharePoint team site with an Out Of Office Calendar that already has a workflow integrated months before I arrived at this company. The calendar basically uses a pending/approved status on the calendar itself, and upon clicking on the pending/approved, I am redirected to a "Page not found" page. What I'm trying to do is go into the workflow to observe the settings and see if there are perhaps any errors that could be fixed. When I look at the toolbar on any page, I can't find the Flow icon! All that's displayed are "New, upload, sync, Export to Excel, and horizontal ellipses." Is there a way I can add Flow to this toolbar?
Furthermore, when I go to workflow settings the message is, "This workflow cannot be customized from the browser. Use a SharePoint-compatible workflow editing tool, such as Microsoft SharePoint Designer, to edit this workflow." My supervisor has told me that the workflow was created by a contractor and that that contractor used MS Flow with the OOO Calendar. What can I do to edit the settings?