How can I change the child component state from parent when the parent passing the same value to child continuously?

Question

Here is my code:

Parent.js

import { useReducer } from 'react';
import Child from "./Child";
let reducer = (state, action) => {
    let result = { ...state };
    switch (action.type) {
        case "backward":
        case "forward":
            result.action=action.type;
            break;
        default:
            break;
    }
    return result;
}
export default function Parent() {
    const [objList, updateObjList] = useReducer(reducer, { action: "init", initValue: 1 });
    let forward = () => {
        updateObjList({ type: "forward" });
    }
    let backward = () => {
        updateObjList({ type: "backward" })
    }
    return (
        <>
            <Child
                action={objList.action}
                initValue={objList.initValue}
            />
            <div className='mt-2'>
                <button className='me-2' onClick={forward}>+</button>
                <button onClick={backward}>-</button>
            </div>
        </>
    )
}

Child.js

import { useEffect,useReducer } from 'react';
let reducer = (state, action) => {
    let result = { ...state };
    switch (action.type) {
        case "backward":
            result.oldValue--;
            result.newValue--;
            break;
        case "forward":
            result.oldValue++;
            result.newValue++;
            break;
        case "init":
            result.oldValue=action.value;
            result.newValue=action.value+1;
            break;
        default:
            break;
    }
    return result;
}
export default function Child({action,initValue}){
    const [objList, updateObjList] = useReducer(reducer, {oldValue:null,newValue:null});
    useEffect(()=>{
        switch (action){
            case "init":
                updateObjList({type:"init",value:initValue});
                break;
            case "backward":    
            case "forward":
                updateObjList({ type: action });
                break;    
        }
    },[action])
    return (
        <>
            {objList.oldValue},
            {objList.newValue}
        </>
    )
}

It works fine. Except when the user clicks the plus or minus button more than one time, the child component only responds once.

I want the child component maintain the value, not the parent component.

How can I update the child state continuously?