Frozen chicken vs thawed chicken in the crockpot
You could cook it for less time, but it equally wouldn't make much difference if you just went for the full 6-7 hours, especially if you are using a forgiving cut like thigh.

I would, incidentally, be very wary about putting frozen chicken in a slow cooker. At the low temperatures a slow cooker uses, there is a good chance the chicken will be sitting in the 'danger zone' for longer than 2 hours, increasing the chances of food poisoning drastically.