in short: you have to import also the MX Reflextion module. (https://appstore.home.mendix.com/link/app/69/) This module creates the option to reflext the model on the client side.
After that you can use the Excel importer module to create a template. The easist way is to use a excisting excel as template. In the template you select which entity should be filled with the import.
This How To will guide you through the process in detail: https://docs.mendix.com/howto/integration/importing-excel-documents
There is a section in the academy you can look at https://gettingstarted.mendixcloud.com/link/path/44
try use...C# oledb and excel