You can see if there is an option to open the Excel file with Google sheet by open with option. If there is no such option, then use a different file manager for your Google Drive files which sorts and list document files according to their extension type.
Head over to docs.google.com and choose sheets option from left slider menu. It will show all files which can open with Google sheets including xls, ofx, and all other Excel file formats.
This method is easy and you don't need to enable convert option from your Google Drive's setting, You can try this method to Microsoft Office Excel Files to Google Sheets File Format.