They may not even meet in the Champions League as a whole. Their first match in the EPL was strange because they dominated, shot at the goal, but were unable to break through the defense despite their colossal dominance. In the Champions League, this would be a critical mistake, and they cannot afford to make it. I think they understand this.
Changes are needed by every player because in their first Premier League match, they seemed to have lost their best form. The coach must evaluate their failure to penetrate the opposing defense so that when they face similar problems in future matches, they have options. In the Champions League, Chelsea will certainly face a much more evenly matched opponent, so they need a player who can make a difference when their front line is struggling to score goals. This is the kind of player Chelsea needs when they are having trouble scoring goals, so matches don't end in draws or losses.
I am sure that nothing will change if they have one additional player who can score. It's not just about one player, but about the team itself and their tactics. What's the point of having a goal scorer if they can't pass the ball well to him so that he has minimal problems on his way to the goal? That's why they need more in-depth work than just a player at the forefront, which they already have.