This sounds like it could be a few different possibilities. A photo will help me to see the issue, and better help me to recommend a solution.
The first thing to check will be nutrient levels. Deficiencies in magnesium, calcium, potassium, and phosphorus can all show these symptoms.
Next, will be fungal issues. Do leaves, or branches also have spots that are black or brown, or maybe rusty looking stuff on the leaves? This could indicate a fungal infection.
Applying dolomitic lime and wettable sulfur together can help kill off an infection, as well as supplement sulfur, calcium and magnesium for fruit formation.
Applying a fruit tree fertilizer once or twice per year will help keep the tree healthy, and ensure that there are plenty of nutrients in the soil.
This article will give you more information on the care of these trees: https://www.gardeningknowhow.com/edible/fruits/soursop/soursop-tree-care.htm