Just make another member variable, like the others
public String guessConvert;
and set that variable in a constructor.
public Engine(Player player) {
guessConvert = player.userGuess;
}
or in a Setter Method:
public void SetGuessConvert(Player player)
{
guessConvert = player.userGuess;
}
You might want to hold a reference to that Player
object as a member variable, if you need to refer to it elsewhere in your code.