It’s said to be part of the challenge “Elderly Assistance”. You’re supposed to scare the birds/ducks away by throwing something at them, then the doctor by the river would leave the place and go to Janus’s house.
But I just couldn’t make it happen. First of all, there’s no duck or bird around the doctor by the river. There are some birds around but far away (some are cross the road). And second, I tried dozens of times throwing things everywhere near the doctor - some to his back, some by the river side and some into the water, and even nearly to the other side of the river, and none of it drove the doctor away. He would quickly get back to his pose and kept on talking to birds (though you can’t see any).
I played this level through Hitman 3 on Epic Game platform, and I can’t figure out how to deal with it.