An external user is a user imported from an LDAP server (see Importing users). You cannot edit the external user's information such as name, department etc. because Teamwork Cloud (TWCloud) only retrieved them when it imported the LDAP user as the external user. But, you can update the external user's information using the resynchonize feature in TWCloud. The Resynchronize dialog requires you to select the LDAP realm from which the external user was imported, and then allows you to update the selected external user information in TWCloud by synchronizing it with the matching LDAP user information on the LDAP server.
You can also use the Import LDAP user page to synchronize external user information. You need to specify both the LDAP realm and the keyword in the Query box. If you cannot provide a specific username, you can type * (asterisk) in the Query box to list all of the external users imported from LDAP servers.
To update an external user information using the Resynchronize dialog
The section Importing users also explains that when you import an LDAP user whose name is the same as that of the existing external user you have in TWCloud, it will automatically update the external user's information with that of the LDAP user.
To update an external user information through the Import LDAP users page
Alternatively, you can update the external user information by converting it to internal user and converting it anew to external user.