In order to convert the Excel Worksheet to IIF format, I recommend you use CSV2IIF software developed by ProperSoft. Firstly, open the Excel document and export it on your desktop to CSV format. You can do that if you click Save As from the File menu and then select .csv from the drop-down list. Download and install the CSV2IIF software, open the CSV file and export it to IIF following the instructions that you can find on the official page. After that, use the steps provided by Intuit to open the IIF file on QuickBooks.