Before importing, you'll need to convert your Excel XLSX document to a format called .CSV, also know as "Comma Delimited." Think of this format as a generic version of Excel.
Here's how to do it:
Open the Excel file and go to FILE>SAVE AS.
Based on your version of Excel, on the next screen you may need to click on Save As Type.
Select the file type called .CSV (Comma Delimited). Then click Save.
Excel will display a pop-up box asking you if you want to keep using the CSV format. Click Yes.