Derive Time-Domain Biquad Coefficients from Z-Domain
I'm not entirely sure what you are asking but if your Z-domain representation is
$$H(z) = \frac{b_0+b_1 z^{-1}+b_2 z^{-2}}{a_0+a_1 z^{-1}+a_2 z^{-2}}$$
Then your difference equation is
$$a_0 \cdot y[n] + a_1 \cdot y[n-1] + a_2 \cdot y[n-2] = b_0 \cdot x[n] + b_1 \cdot x[n-1] + b_2 \cdot x[n-2]$$
And solving for $y[n]$ we get
$$y[n] = \frac{1}{a_0}(b_0 \cdot x[n] + b_1 \cdot x[n-1] + b_2 \cdot x[n-2] - a_1 \cdot y[n-1] - a_2 \cdot y[n-2]) $$