If what you are saying is the proportion in your sample was originally 0.04/0.96, then you oversampled to get 0.3/0.7, then in a Decisions node, you should have entered the original prior probabilities as the Adjusted Priors. Then if you look in the score code in the Score node, you should see lines like this doing the adjustment of the posterior probabilities:
*** Update Posterior Probabilities;
P_BAD1 = P_BAD1 * 0.04 / 0.3;
P_BAD0 = P_BAD0 * 0.96 / 0.7;
drop _sum; _sum = P_BAD1 + P_BAD0 ;