How do I apply predicted test dataset on random unlabeled validation data set

I have trained model (Decision Tree) based on training set (0.8) and tested the trained model on test dataset (0.2) and got the accuracy results with performance operator.
However, I have random unlabeled validation dataset which i.e external example set, and I want to apply the trained and tested model on validation dataset and get the accuracy and confidence interval results for that validation set.
How do I proceed? Please suggest as soon as possible.