accidently changed player of the TOTY part

I picked Marquinhos from the three options without knowing that I have to score some goals with the chosen player. It wouldn't be an issue, because there are easy ways to score enough goals in FCM even with defenders.

But I accidently changed Marquinhos for "puzzle pieces" before I noticed that I need him to complete all the challenges in the TOTY part of the Anniversary-Event.

So I decided to buy Palmer from the market. I saw, that a lot of other players wanted to buy him, so I thought my goals with the bought Palmer will count. I got disappointed. I paid more than a billion coins for nothing.

I hope you can bring a solution for my problem.

For the future, it would be great if the "needed" players can't be changed or sold, so that every player can be sure to fulfill all of the challenges. Maybe you can mark them as long as they are necessary for the game progress.