Can't Add Tablets Back In To MDM

[RRLowery]

Hi All, 

So a bit of backstory... 
I have taken over the running of a primary school, that uses Meraki as its MDM solution. 
The school used to be two schools that merged so their IT is a bit all over the place. 

It appears that some tablets were "misplaced" during the merge and someone deleted them from the Meraki Dashboard assuming they were lost for good. They were then located, but no one knew the login credentials, so they tried to reset them. 

So now I have about 5 tablets, that are no longer in the Meraki console, but the reset failed as the tablets still think they're part of the MDM and are asking for an email address, that no one knows. 

Can anyone advise, how I can get these tablets (Samsung Galaxy Tab A - SM-T510) back to a state where I can add them back in to Meraki and make them usable?

Thanks in advance for any assistance. 

[PaulF]

You won't get this right first time, as it takes some real concentration, but: https://www.wikihow.com/Enter-Recovery-Mode-on-Android-Smartphones

[RRLowery]

Hi, 

I've tried this. There is no recovery mode on the Samsung T290 (another model I've got that's stuck in limbo)
If I reset everything looks fine, then I try to sign in and get "This device was reset. To continue, sign in with a google account that was previously synced on this device"

As these tablets are from a school that doesn't exist anymore, I don't know what email addresses were used, nor do I have access to them any more. 

Regards
Rik