One way to create a CSV file that can be opened with Excel would be setting this parameters when calling the report, to generate its output to a delimited file
DESNAME= 'YourFile.csv '
You could also use some third party tool to make the export.
And other option would be to create the excel file from Forms. How to do this has been asked before. Here’s a question about this:
How to call Microsoft Excel from Oracle Reports/Forms 6i