How to use string as object in redux react

I’ve redux store which looks like below.

store = {
    a: {
        b: { value: "" }
    },
    c: { ... }
};

From my component, I want to pass like below to minipulate value of b.

dispatch(doSomething({ value: 'my-value', place: "a.b" });

And, in my reducers,

doSomething: (state, action) => {
    const { value, place } = action.payload;
    state[place].value = value; // here, i want to refere -> state.a.b.value = value;
}

How can I achieve it?