You have already created a data type that you want to reference from your message type.
Familiarize yourself with the basics of message types.
More information: Message Type
Create a message type on the design maintenance screen of the ES Builder.
More information: Creating an Object
Enter a description for your message type.
The default setting for XML Namespace is the Repository namespace. If the message type has been copied to another namespace, overwrite the default setting.
Reference a data type, either by entering the corresponding name and namespace of the data type in the frame Data Type, or by using input help.
Save your changes.