Thank you for posting here in the Community, @tergeoboa.

I’m here to make sure your you're able to open the IIF file. For me to provide the best solution, I need to gather more data about the issue.

Can you share with me what happened when you attempt to open it? Any additional information you can add will help ensure a timely solution.

While waiting for the details, let’s try following these steps:

1. Open Microsoft Excel.
2. Click the File menu.
3. Select Open. 
4. Select the IIF file.
5. Click Open. 
6. Select Next twice and Finish in the Text Import Wizard.
7. Make the necessary edits.
8. Save changes.

I suggest visiting the Export, import, and edit IIF files article. It also contains an overview of importing and exporting Intuit Interchange Format files and how you can edit them.

Reach out to me anytime if you have any other concerns. I’ll be right here ready to help you. Enjoy the rest of the day.