Currently, there is no way to move devices between SEP Mobile tenants through the portal.
In order to move a device enrolled in SEP Mobile to a different environment, the app must be fully removed from the device. Then the device must re-enrolled to the new environment using a supported enrollment method.
Note that depending on how the enrollment options for a particular environment are configured, additional configuration within the management portal or your MDM solution may be necessary before the device can be enrolled to the new environment.
For further details on device enrollment, please review the following document: