Predict output sequence one at a time with feedback
I assume, that your data looks somehow like this (a pair of question and answer)

Question,Answer
How are you?,I'm fine.
How are you?,OK.
How are you?,Very well, thanks.


I'd suggest to transform it in three features: Question  (remains the same), 
InputSeq is the prefix of the answer generated in all possible lengths between zero and the number of words minus one.

Finally the NextWord is the expected result.

So for your initial data you ends with the following setup.

Question, InputSeq, NextWord
How are you,,I'm
How are you,I'm,fine
How are you,,OK
How are you,,Very
How are you,Very,well
How are you,Very well,thanks


The model takes Question and InputSeq   as features and predicts the NextWord.