For On-Premises Exchange
When restoring to on-premises Exchange server, specify Global Catalog access credentials. Enter the corresponding domain name and specify the user account having sufficient access rights to connect to the Active Directory and to the target Exchange Server. You can use your current account or specify another one 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
When restoring to Exchange Online, specify the account to connect to the target Exchange. You can use your current account or provide another one in the username>@<organization>.onmicrosoft.com format. Make sure the account has sufficient access rights to access the target.