The librarian who handed you the right book at the right time may have changed how you think. Go back and tell them.

A book arriving at the right moment can reorganize what you believe is possible, and somebody chose that moment. Matching a person to a book is a real skill: a guess about who you are and what you were ready to be interested in, made in about ninety seconds at a desk. They almost never learn whether the guess worked.

Go back and say which book it was and what it did, even if it was years ago. Email works if the visit does not. Then ask for another one, since the first good recommendation is usually not the last they have.