As far as I understand, Robert_F is correct.
Databases are tied to an account and cannot be migrated between accounts. So, you cannot restore a database backup made on RoonCore/ Account1 onto a RoonCore /Account2.
See, post by Dylan here: Restoring backup from one account under a different account, keep customisation - #2 by dylan Quoted beneath:
A Roon backup can only be restored on a Core using the same account that the backup was created on. There is no way to restore a database on another account. You have our apologies for any inconvenience this may cause. We appreciate the feedback!
@Alain_Grimard I would suggest forgoing a second account and just move the active core between locations as needed. This will allow you to restore a backup from one core to the other, as Robert_F does.
This, of course, means both Cores cannot be active at the same time since the account will only be active on one or the other.