I had to re-install Raspbian OS and now it has new SSH key. SSH clients usually let ignore this fact and save the new key, but not now.
Mathematica gives no way to go if the Host Key was changed. I get an error
SSH received a different Host Key while launching kernel 'Raspberry Pi'. Error code = 124.
when trying to start remote kernel and I have found no any information about where is the Mathematica's SSH client on Windows... I just need to clear known hosts...
The easy way is to change Raspberry's IP, but it's far less interesting, moreover not always possible