New mutagens and a new set of armor - how to start quests? (The Witcher 3: Wild Hunt)

Started playing Blood and Wine. At the beginning of the game, near the mill, a window appears to appear on the left. It said that in Toussaint there is an excellent blacksmith who can forge cool armor, and there is some kind of professor, there was something related to mutagens. It was written that a messenger would come. So when will the messenger appear? As far as I understand, you can't start quests without him?