Ther isn’t any Kaffarah for that. You either had to do it as it was necessary and advised by trustworthy doctors or you did it without any need for that. If you had done it through the advice of the doctors, there is no sin on you. But if you had done it without any legitimate reason, you should repent and ask Allah for forgiveness and there is no Kaffarah for that.

We have done family planning operation, having 2 daughters-1 son, as I was having complication during the last baby it was cesarian and had diabetics, had low bp, had to take 2 units of blood +thyroid , so wat is the kaffara that I can do ?