Some Karma can be changed and some cannot.
When you prepare a dessert, if sugar or ghee is too little, you can add more. If some ingredient is too much, it can all be adjusted and repaired. But once it is cooked, it cannot be reversed.
Milk can become sweet yoghurt or sour yoghurt and your yoghurt can be sweetened. But neither can be reversed back to milk.
Sanchita Karma can be changed and adjusted by spiritual practices. Prarabdha Karma cannot be changed. And Satsang burns the seed of all negative karmas before they are given a chance to sprout.