How do I get my father's online banking details?

First of all, I apologize if I'm in the wrong place with this topic, I'll try to keep it short. My mother kicked my father out of the apartment we shared and he is now staying with his brother abroad. When he got there, he probably had problems with his smartphone, or more precisely the roaming, and some joker in a dubious cell phone store reset it to factory settings. Of course, he was kicked out of Sparkasse online banking. I h