Can someone explain to me how to use a predictive model to predict something other than the training set
Yes, you can predict who will open a loan with this model. You have to keep several things in mind. The model expects the new data to be from the same distribution as the training data, meaning the variables have the same distribution and targets as well.
You can not train on one set where 3% opened a loan and then predict on a set where you expect that 90% open a loan. This data is then too different for the model to accurately predict on.
Remember that your model only has 90% accuracy, so it is not guaranteed that a specific costumer will open a loan when the model predicts so.