You might want to be a bit more specific here – what kind of report are you talking about?
I assume you would like to extract data into Excel from a data grid, in which case you can use built-in functionality to do that.
https://forum.mendix.com/link/questions/107644
For more in-depth reports you might want to look into Excel exporter module on the marketplace
https://docs.mendix.com/howto/integration/using-the-excel-exporter/