What to do after GridSearchCV()?
You can use grid_obj.predict(X) or grid_obj.best_estimator_.predict(X) to use the tuned estimator. However, I suggest you to get this _best_estimator and train it again with the full set of data, because in GridSearchCV, you train with K-1 folds and you lost 1 fold to test. More data, better estimates, right?