bivariate conditional joint sensor model

Question

I am struggling to find $P\left( V_t | z \right)$ from $P\left( V_t | z , V_p \right)$. Here $z$ and $V_p$ are independent variables.

p_sensor = (1 / sqrt(2 * pi * r_noise)) * exp(-(Voc(z) - V_t - V_p - I * R0)^2/(2 * r_noise));

I need this $P\left( V_t | z \right)$ sensor model from the above model. How can I get it? Many thanks in advance!