Some karma can be changed and some cannot.
When you prepare halwa, if sugar is less or ghee is less, water more or less, it can all be adjusted, repaired. But once soji is cooked, it cannot be reversed.
If the buttermilk is sour, milk can be added, salt can be added to make it drinkable. But it can never be reversed back to milk.
Prabdha karma cannot be changed. Sanchita karma can be changed by spiritual practices. Satsang burns the seed of all negative karma.
When you praise someone, you take on their good karma. When you blame someone you take on their bad karma.
Know this and surrender both good and bad karma to the Divine and be free.
~ (Sri Sri Ravi Shankar)