First you need to import the Excel data into your Mendix application, you can do this using the Excel importer module (https://appstore.home.mendix.com/link/app/72/). READ the information on the Documentation Tab very well, because there are some dependencies. 

Once you have done that, follow these steps https://docs.mendix.com/howto/integration/importing-excel-documents

After these instrucution you are able to import data from your Excel sheet into Mendix. After that you should be able to use default widgets (like Dropdown (https://docs.mendix.com/refguide/drop-down) and reference selector (https://docs.mendix.com/refguide/reference-selector)).