It sounds like they have excluded the causes of LBBB that they would need to do something about, such as a narrowed coronary artery, a sticky/leaking valve, high blood pressure, various sorts of heart muscle disease, and a very slow heart rate. It would be uncommon to be born with this, and if so it would almost always be associated with some sort of structural heart disease - sticky/leaking valves and so on.
But they have not answered the question, or more specifically revealed to you, why you have this.