Use GPT2LMHeadModel to start a new sentence

I am using GPT2LMHeadModel to change the way GPT2 choose the next word in a sentence. At this point, I have to give the initial part of the sentence and GTP2 starts to predict the better next word.

I want GPT2 to read an entire sentence and then start a new one based on that (like it does with translation). Is there any kind of parameter that I need to set up in order to make GPT2 start a sentence from zero, not complete an initial one?