I haven't tried any of the computer apps, but Caustic Editor for Volca Sample is free on both iOS and Android

The best way to deal with this is to use the Caustic or AudioPocket editor and identify some of the longer factory samples (1 second or longer) and target those to be replaced.

This is a very fun unit and the caustic editor for iOS is definitely nicer than Korg's

For example, I recorded a simple C2 note in a great app called iFretless Bass, sent it to the Caustic Volca Editor via AudioShare, and had a pitch tuned electric bass sound available on my Sample, and the whole process took maybe a couple of minutes

This is a very fun unit and the caustic editor for iOS is definitely nicer than Korg's

I haven't tried any of the computer apps, but Caustic Editor for Volca Sample is free on both iOS and Android

Once you have your samples in Caustic Editor and tweaked however you want them, you simply designate specific slots for each of them (the Volca has sample slots 00 through 99), connect an audio cable from the headphone jack to the sync in port of the Volca, and hit the sync button

On iOS, I use AudioShare (it also supports AudioCopy) to get samples into the Caustic Editor app, and it has tools for trimming samples and such as well as a whole set of effects you can apply to your samples to get them ready for the Volca -- chorus, compressor, etc

The Caustic Volca Editor easily links up with an app called AudioShare to import samples stored on your device, or imported from a cloud service like DropBox.