I have serial access, but How I can login using ssh ?
Which OS are you running on the Hikey960 ?
hikey960:/ $ uname -a
Linux localhost 4.9.43-g3102c15143f0 #1 SMP PREEMPT Sun Aug 20 01:41:34 UTC 2017 aarch64
Depending what you really want to do, the easier way could be to use ADB over USB or TCP/IP.
If you really need ssh, you can try: