Program Mcpe addon. Enchant?

I want to make an exact enchantment on an item with an addon eg sharpness 3. In this txt it is random. What do I have to change?

{

"type": "item",

"name": "minecraft: diamond_chestplate",

"weight": 3,

"functions": [

{

"function": "enchant_with_levels",

"treasure": true,

"levels": {

"min": 20,

"max": 39

Unfortunately I do not know myself from sry