Specify the user account to access the target Exchange server according to the following.
For On-Premises Exchange
When restoring to on-premises Exchange server, specify Global Catalog and access credentials.
Enter the corresponding domain name and specify user account with sufficient permission level to connect to the Active Directory and target Exchange Server. You can use the account currently logged on, or specify another one in the domain\username format. Make sure the account you specify at this step has sufficient permission level to restore objects in the target domain. Click Next to proceed with mailbox selection.
For Exchange Online
When restoring to Exchange Online, specify the account to connect to the target Exchange server. You can use the account currently logged on, or specific account in the email@example.com format. Make sure it has sufficient rights to access the target. Click Next to proceed with mailbox selection.