How I can fix, a damage done to files that were open for writing at the time of the computer crash.
You probably can’t repair it. Just zap it.
You could try chkfsys.
Let me try to give you the whole story.
If the file has some kind of irretrievable data, then you
first need to do some spielunking in the file system.
This was documented with QNX 4, but I don’t know where or
if it is with QNX 6.
If you don’t want the data at all, or can restore it, then
run zap on the file and run chkfsys.
Otherwise run chkfsys. At this point your file could be
gone, empty, but it may be restored.
In any case, the file system is now sane.