Update specific value in state array of object with context api

So I have a state array containing objects, I want to update a specific value of a given object, given the object index.

const initialState = {
cars:[ {name:  "golf", speed: 14, price:444}, { name:"benz", speed: 15, price:6666}]

}

so this is a sample state, what I want to do is, given the index of the object(e.g the second object) I want to update the speed to 15

my Action is

const setSpeed = (index) => {
    console.log(index);
    dispatch({
      type: SET_SPEED,
      payload: {
        respond: index,
      },
    });
  };

Above is my action that dispatches a type of SET_SPEED, and the index of the object as a payload.

I'm trying to write a reducer that update the speed by one given the index of the object