A read-only version of the spreadsheet appears below. On the top right corner of this display is a black square containing an upward-pointing arrow. Hover over that and the words "Pop-out" will appear. Click on it.
The screen will then change to offer the opportunity to "Open with Google Sheets." If you DO NOT have access to Microsoft's Excel on your device, this is a good option to choose (by clicking on it).
If you DO have access to Excel, click on the icon immediately to the right of the "Open with Google Sheets" option. You can then save the file to your account on Google Drive. If you'd prefer to download the file to your device, click on the next icon to the right, "Open Original."