having just modified a report today, the process is:
Database / Set Database Location
Create New Connection
ADO.NET(XML)
select the file that is the desired XSD file
report now has a dataschema (and perhaps data, depends if your XSD file has the XML data or just the schema).
If the XSD file only contains schema information, your report will be blank as it has no data. I write out the XML data along with the XSD schema in one file, then I have both schema and test data.
HTH