Opening a .tmp file in Excel can be a bit tricky, but it is possible. Here are the steps you can follow:

1. Open Excel and click on the "File" tab.
2. Click on "Open" and navigate to the folder where the .tmp file is located.
3. In the "Open" dialog box, change the file type to "All Files (*.*)" to see all files in the folder.
4. Locate the .tmp file you want to open and select it.
5. Click on the drop-down arrow next to the "Open" button and select "Open and Repair".
6. Choose the repair option that best suits your needs. You can choose to repair the file, extract data, or cancel the operation.

If the above steps do not work, you can try renaming the .tmp file to .xls or .xlsx and then try opening it in Excel. To do this, right-click on the .tmp file, select "Rename", and change the file extension to .xls or .xlsx.

If none of these methods work, it is possible that the .tmp file is corrupt and cannot be recovered. In this case, you may need to try a file recovery tool or contact a professional data recovery service for assistance.