On the Credentials page, in the Enter your on-premises account credentials section, select Use current %BRAND_WINDOWS_SHORT% ...

On the Credentials page, in the Enter your on-premises account credentials section, select Use current %BRAND_WINDOWS_SHORT% credentials to have the wizard use the account with which you're logged in. If you want to specify a different set of credentials, unselect Use current %BRAND_WINDOWS_SHORT% credentials and type the username and password of an Active Directory account you want to use. Whichever credentials you use, the account must be a member of the Enterprise Admins security group and have access to your on-premises Active Directory and %BRAND_EXCHANGE_ONLINE_SHORT% 2010 servers.