Hi @Joerg George Bolik ,
Welcome to the community!
Please visit the below link and follow the steps carefully!
https://help.trello.com/article/1079-troubleshooting-for-the-android-app
I hope after following the steps your problem will be solved! If your problem still not solved you can ask Trello support HERE
It looks like you're new here. Sign in or register to get started.