For On-Premises Exchange
If you are restoring to on-premises Exchange server, specify Global Catalog access credentials. Enter corresponding domain name and specify user account with sufficient rights to connect to Active Directory and target Exchange Server. You can use the account currently logged on, or specify another account in the domain/username format. Make sure the account you select at this step has sufficient rights to restore objects in the target domain.
For Exchange Online
If you are restoring to Exchange Online, specify account for connection with target Exchange. You can use the account currently logged on, or specific account in the username>@<organization>.onmicrosoft.com format. Make sure it has sufficient rights to target.