As far as I can say, you just have to change your examination plan with a signature of your mentor and have to inform the Prüfungsamt about this, of course (see §11(3)). So, pick up your examination plan from the Prüfungsamt, make the changes with your mentor, and send it back to the Prüfungsamt.
I understand that the module you want to drop is in the supplementary block, which means that you can replace it with a lot of other modules. As far as I know, the failed attempt is then waived in contrast to modules of the theory blocks and the specialization. If you exchange modules in the theory blocks or the specialization, the failed attempts are counted for the new module.
In any case, module have to be passed with the three attempts.
