Making a average plot on the posterior plot _ ppc

The following sample from the posterior_predictive along with the data points give me the attached plot. I want to add mean/average plot of sample_posterior_predictive on the same plot.
third plot would be average posterior_predictive. any ideas?

#generating sample_posterior_predictive
y_pred_g = pm.sample_posterior_predictive(trace_g_pt3, 1000, model_g)


#making plots of the sample_posterior_predictive
data_ppc = az.from_pymc3(trace=trace_g_pt3, posterior_predictive=y_pred_g)
ax = az.plot_ppc(data_ppc, figsize=(12, 6), mean=False)