My watch crashed near the end of my activity and after a soft reset I got the Blue Triangle of Dead, making a hard reset the only option to get it working again.
I managed to recover the .fit file using data recovery software, but it seems to be corrupt, because I it won't work anywhere.
Much appreciated if someone can fix this one for me!! 
but it seems to be corrupt
That is usually the case, sometimes beyond repair. In this case Fit File Repair Tool returned the following message, "332,932 bytes of the file are corrupted and could not be repaired," which is about 78% of the 425 kB fit file. So unfortunately there's nothing I can do with this as it is. 
It's also not possible to make it at least into a readable file, or a cvc file or something in which I could maybe still do some manual adjusting?
