Thanks for the initial help, I have managed to reset everything except for the Terminal. (where python code is written) I moved and duplicated the wrong files so when I try to re begin the course from the intro page the first function does not work as there is no file found…because I mixed them up.
Also this message pops up:
There are packages with the same name. Check the files package.xml and CMakeLists.txt of each package in your workspace. After fixing it, the simulation will be automatically restarted in some seconds.