ABM - iPhone activation & Sticky MDM profile

ABM is setup with 2 MDM servers, one as default.

Occasionally new iphones need to be assigned to 2nd MDM but this is not done on time and user switches on the iphone it activates and gets default MDM and Remote Management screen of that MDM server and login is required. The phone never completes setup, so not possible to RESET.

I've tried making the correct change in ABM, switching off the phone and trying after 24 hours - no luck, still has wrong MDM.

So far the fix is either reset phone on Configurator or iTunes. (Issues with logistics and admin permissions prevent end user from doing this themselves)

Question:

1. Is there a way to force the iPhone to re-activate and pull down correct MDM server? Is it a case of leaving it switched off longer ?