Where to change city of residence in passport? (Singapore)

Hi,

Does anybody know where I can or need to change the address of residence in my German passport? At the moment, there is Munich stated and I would need to change this to Singapore in order to shop tax free in Germany.

Is that just possible with the German embassy in Singapore or does anybody know if thats as well possible in Germany?

As I'm in Munich at the moment I would love to do it here and to bring some tax free items to Singapore :-)

Thanks!!