已知函数 $f\left(x\right)=\sqrt{2}\cos (x-\frac{\pi }{12}),x\in R$．
(1) 求 $f\left(\frac{\pi }{3}\right)$的值；
(2) 若 $\cos \theta =\frac{3}{5},\theta \in (\frac{3\pi }{2},2\pi )$，求 $f(\theta -\frac{\pi }{6})$．