Have a look at: https://docs.pymc.io/notebooks/posterior_predictive.html
You can use:
preds = pm.sample_ppc(trace, model=model, samples=100)
y_preds = preds['y']
to produce sample predictions on the data you used to train the model.
If you need to make predictions using other data as input, you can swap the data into ann_input since you use a shared Theano layer, and then run the sample_ppc