When an account establishes a trust relationship with your account, you become a delegated party. The IAM users granted agency permissions can switch to the delegating domain name and manage resources under the account based on the granted permissions.
The IAM user created in "Assigning Permissions to an IAM User (by a Delegated Party)" has permission to manage agencies and switch roles.
After you enter the domain name, the agencies created under this account will be automatically displayed after you click the agency name text box. Select an authorized one from the drop-down list.
Move the cursor to the username in the upper right corner and choose Switch Role.