You get the option to do this once the recording has been made - you’ll see the waveform and a ‘trim’ option below. You can trim multiple slices from that recording, saving each one, and returning to the recording (Have a quick look on youtube for a Digitakt tutorial that’ll show this, or read the manual). Once you’ve saved the file, you can’t further edit it.
You can’t edit samples once they’re saved into the drive - that goes for ones recorded via inputs, and for ones sent by computer.
It’d be nice to have the ability to further edit samples, but as of now, we don’t…