There's no tuning involved at all in order to get your VCR to record from the digibox.
When you were using your VCR to record analogue TV transmissions (possibly while watching a different channel on your TV) the VCR used its own, built-in, analogue tuner to process the incoming signal and then send the output to the videotape. You could watch a different channel at the same time because your TV used its own built-in analogue tuner to send a signal to its screen. You've now only got a single digital tuner (in the digibox), so you won't be able to watch one digital channel while recording another. Further, since the tuner isn't inside the VCR, no amount of tuning of the VCR will persuade it to directly receive and record digital channels. The trick is to get the VCR to record the output of the digibox by switching it to record 'AV' (rather than any numbered channel).
So you plug your aerial into your digibox. Then connect the output of the digibox, using a Scart cable, to the input of your VCR. Assuming that your VCR has got two Scart sockets (and that your TV also has a Scart socket), connect the VCR output to the TV with another Scart lead. To record a program on your VCR, set the timer (if required) on your VCR and programme it to record from 'AV' (rather than from a numbered channel). Make your channel selection using the digibox (and remember to leave the digibox switched on when making the recording).
If your TV doesn't have a Scart socket, or your VCR only has one Scart socket, you can replace the second Scart lead with an aerial fly-lead between the VCR output and the TV's aerial socket. If you can already watch videos played back on the VCR no tuning will be needed. Otherwise the usual way of doing things is to tune the TV to match the signal from the VCR. (If you try to do it the other way round you'll need to tune the VCR's output, using a screwdriver, via the small control normally found at the back of the box.