There is no need to add the values after performing the train_test_split as the output is an array. You can simply try with the below code:
Xtrain = Xtrain.reshape(-1,1)
Xtest = Xtest.reshape(-1,1)
If you want to unleash your potential in this competitive field, please visit the Machine Learning Training page for more information, where you can find the and as well.
For more updates on the latest courses stay tuned to HKR Trainings.