Both .iif to .qbw files come from accounting software called QuickBooks by Intuit, but each of the file types serves a bit different purpose so actual iif to qbw conversion is not very likely. What you can do however is import .iff file to QuickBooks and perhaps some data from it are added to the company data which can then be exported and saved as .qbw file. But it's not a file conversion in proper sense.
If you for some reason need or struggle with this export, it might be best to consult Intuit help files or contact their support for assistance.
Updated: October 10, 2023