Vitamin b for plants and trees
That’s a great question and one we don’t yet have an answer to. Mainstream agriculture does not currently apply vitamins to plants.
The yellowing could be one of several nutrient deficiencies including nitrogen if the old leaves are yellow and the young ones green. Sulfur is the opposite. Yellowing across the whole plant suggest iron. Interveinal chlorosis is generally magnesium. Take some leaves and photos of the whole plant and symptomatic leaves to your local Extention office.