Hope you are using IS6.01 server.
You can install the EDI Document type 4010 820 from the
WmEDIforTN home page in the ISAdminBrowser/Package/ Management.
This will install EDI 4010 820 DocumentType in TN and will create Schema,Dictionary in the developer.So open Package WmEDIforTN/EDIFFSchemaEDIFFSchema.X12.V4010:T820(Schema),Click on the T820 and there is an Icon under the FlatFileStructure tab, for (CreateDocumentType) which will give you the T820DT (webMethods record structure).
Its pretty straight forward.
HTH.
#Integration-Server-and-ESB#webMethods#edi