Hi
This worked for us courtesy of Meraki Suppot
Navigate to "Device Administrators" within the Settings application on each device and disable the Meraki SM app as a Device Administrator. Next, you will want to uninstall the Meraki SM app from each client. At this point, the devices should no longer be bound to Systems Manager. Additionally, if you would also like to remove the clients from your Dashboard, you can then also navigate to Systems Manager > Clients and select the devices and then use the "Delete" option.
When we then logged into Google Admin dashboard there was an Unbind option in the EMM options.
Good luck
Paul