It is correct that we cannot convert anyone to Christ. I was speaking about converting one’s soteriology to Calvinism, which I would not consider exactly the same. But yes—the Holy Spirit clearly must draw those called by the Father to repentance and the need for a Savior.
Then you should start talking to Calvinists. Even though we know that God has determined who will be in heaven, we do not know the means by which He chooses to do it, therefore, we MUST be dilegent in telling others about Jesus. It is what we are called to do. To not do so would be sinful.