increament(e, item){
  let qty = e.target.previousElementSibling.textContent;
  qty++;
  e.target.previousElementSibling.textContent = qty;
  this.props.changePrice(item);
}

<div>
  <input onClick={(e) =>this.decreament(e)} type="submit" value="-"/>
  <span>1</span>
  <input onClick={(e) => this.increament(e, item)} type="submit" value="+"/>
</div>

function mapStateToProps(state){
   return({
     itemlist: state.rootReducer
   })
 }
function mapDispatchToProps(dispatch) {
   return({
      removeItem: (item)=>{
        dispatch({type: 'removeCart', payload: item})
      },
      changePrice: (item)=>{
        dispatch({type: 'changePrice', payload: item})
      }
   })
 }
export default connect(mapStateToProps, mapDispatchToProps)(Cart);

const changePrice = (itemArray, item)=>{
  let newObject = {};
  let filteredObject = itemArray.filter(reduxItem => reduxItem.id === item.id);
  let newprice = filteredObject[0].price + filteredObject[0].price;
  filteredObject[0].price = newprice;
  newObject = filteredObject;
  const something = ([...itemArray, newObject]);
  return something;
}
const reducer = (state = [], action) =>{
  switch (action.type) {
    case 'Add':
      return [...state, action.payload]
    case 'removeCart':
      const targetItemIndex = state.indexOf(action.payload);
      return state.filter((item, index) => index !== targetItemIndex)
    case 'changePrice':
         return changePrice(state, action.payload)
    default:
      return state;
  }
}
export default reducer;