shared ipad setup

shared ipad setup

I would like to add shared ipad functionality to some of our ipads managed in MDMplus.  I have read https://www.manageengine.com/mobile-device-management/help/asset_management/mdm_shared_ipads.html but cannot find any of the options listed in the document:

I already manage 9 ipads through MDM, they have been enrolled from our ABM already, I have managed them for a year.  Do I need to start again on each ipad to get the setting for "shared ipad" to appear?  The documentation says:
  1. After you have generated the server token , and have uploaded it on the MDM server, click on Device Activation settings and navigate to the Shared iPad option and enable it.
I set up my MDM server token a previously, the ipads are already enrolled.  What do I do if the MDM server has already been setup?  I am happy to deprovision an ipad from MDM and re-enrol in MDM again but I cannot find the "device activation settings" to enable shared ipad.  

Can I enabled "shared ipad" on only two of our ipads or do I need to activate it on all simultaneously?