Store a specific value to a specific attribute in class structure with

I have this simple class structure:

class Animal {
public:
    int x;
    Animal(int x) {
        this->x = x;
    }
}

I am using more threads, so I use <atomic> to handle reading and writing in one variable from more threads.

std::atomic<Animal> animal = Animal(5);
animal.load().x // 5

But how can I store a specific value to a specific attribute?

??? animal.store().x = 10 ???