This question has already been answered about using ODS and Base SAS in the other posting.
If you want to use Web Report Studio, then you have to use WRS menu buttons to export your WRS report to Excel. In this instance, you are NOT using ODS -- you are using internal WRS methods that are controlled within the WRS interface.
If, on the other hand, you want to use the SAS Information Delivery Portal or the SAS Stored Process Web Application to run a Stored Process that will return ODS CSV or ODS TAGSETS.EXCELXP results to a browser, then you will need to use the STPSRV_HEADER function to tell the browser what application to launch when the result file is received.
There are some examples of using STPSRV_HEADER in the Stored Process documentation.