I am not good at knowing what to say when someone is going through death?

If you are religious, then it should be important whether the person facing death has forgiveness for their sins. Try to get a moment where you can speak to the person alone and ask them what they think about God and if they are ready to meet Him and if they would like to pray to Him to ask forgiveness? This person's eternal destiny is in question. Lead them to Christ to get forgiveness of sins.