should I shift a dataset to use it for Time series regression with RNN/LSTM?
Yes, you are making prediction, which means using historical features(such as at time t) to predict the target in the future(say t+1). In many cases, you could use past few timestamps' features(say t-n,t-n+1,...t) to predict. Preprocess your data in the way (X_historical,y_future) in case of data leakage.