You can add a new person with the name "Stephan Schäper, Stefan Thalmann", or you can "Stephan Schäper, Stefan Thalmann" with a person entry that is so far only been referred to by another name (such as a former name or an alias name).
Your choice of the person associated to the publication can be saved in our system, so that no other have to make this choice again. Do you want to save your choice?