This time, his motivations were not as malicious as they were when he led his men with the sole purpose of committing crimes, to put it frankly. This time, the exact opposite would happen. Granny entrusted Klaus with the training of good people b who are trying to make a living, and she wanted someone trustworthy to ensure that they do their jobs properly. Klaus seemed to be exactly that person.
His expectations were low, given that cleaning and maintaining facilities were not the most joyful activities in the world. In fact, they are the polar opposite. But that didn't stop Klaus from coming up with some clever ways to keep the trainees under control. Assuming they respect Granny enough not to upset her, they are unlikely to ignore Klaus's instructions or ignore his role as a supervisor, even if the role is just temporary. And even if they did, Klaus wasn't sure how far he'd go to punish them - or if punishing was the wisest course of action.
In any case, helping someone for the sake of helping, especially an elderly person like Granny, had the promise of being both refreshing and, more importantly, a significant step forward in his redemption journey.