This article explains how to add an I-Series GMS device to a Gmail Account or Android Enterprise

Out of the box, Elo's GMS Android devices that ship with Android 8.1 or above do not display the Google Android Welcome Screen. Similar to older Elo Android devices, they will boot direct to EloView so customers can continue to provision and deploy with no change in procedure.
 
The devices are connected to a generic Gmail account which allows access to the Play Store and associated services.
 
If a customer needs to associate devices to their own Gmail account or complete Android Enterprise enrollment, the device simply needs to be factory reset.
 
This can be completed from Android Settings - System - Reset options - Erase all data
 
Upon reboot, the device will greet the user with the Google Android OOBE and allow these enrollments to occur, if desired.