In InDesign Preferences under the Technology Previews tab tick Publish Online (Preview). The "button" appears at the top next to the type of Workspace.
If it's not appearing in the menu, you probably need to trash your InDesign preferences: Close and relaunch InDesign, and IMMEDIATELY hold down Ctrl + Alt + Shift (Windows) or Cmd + Ctrl + Opt + Shift (Mac), and respond Yes when you are asked if you want to reset your Preferences. (Source: Trouble shooting)
Two more possibilities: The menu only appears when you have a file open.
Also, you may need to go to the CC desktop app. Click on the "gear" icon and choose Preferences > General. Sign Out and sign in again with your Adobe ID.