Yep, the switch is SL-I or II... Didn't know it was for setting the K3 command in case of miss...
I've read that "Vozvrat" should be pressed if the target was missed or after time, and that makes me to think that self destruction is from some kind of iternal clock... Don't remember where, but also read thah NVA officers stopped that clock and achieved almost 80 km shot, which results on colateral damage on the ground... I was wonderning what "Vozvrat" exactly do?

In STAND (normal) radio proxy fuse mode, 300m before the range boresight, K3 command is sent out, to arm the Radio-Proxy fuse.
If the missile avoid the target, and fly further the range boresight, the K3 command is emitted again by the SNR.
When the K3 received second time, the missile will do, what the SL-I/II switch signaled on the launcher.

If you press the VOZVRAT before the missile reached the range boresight, the K3 is signalled twice.