In order to convert the data from QBMB files to CSV format, you would first need to restore the backup and then perform some sort of export in QuickBooks. Just be careful when restoring backups because they usually overwrite the current data.
Convert QuickBooks backup file to Comma Separated Value.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert qbmb to csv on Windows
A business accounting software from Intuit
Convert from qbmb 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.