If any program can someone convert QBW to IIF, it would be QuickBooks from which both of these formats originate. Whenever is this conversion useful or even possible could not be verified.
Convert QuickBooks company data to QuickBooks interchange format file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert qbw to iif on Windows
A business accounting software from Intuit
Convert from qbw file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.