Prior to CatTools version 3.2.0, the DB.UpdateDevice.Text field activity was formally known as Database.Update.Device text field.
If you really are on version 3.0.3, then it may well be the case that the Database.Update.Device text field activity did not exist in that version.
I'd therefore recommend upgrading to the latest release.
Please note: the CatTools on-line help file will only ever relate to the current product release.
For your CatTools version specific help, you should refer to the product built-in help (Help > Contents menu item)