How to increase and deacrease the qty in session

Please someone help!!!!!!!!!!!!

This is my Html and app.js file code

<button class="h-6 pl-2" id="plus" data-plus-id="<%= pizza.item._id %>"><i class="fa fa-plus"
                                aria-hidden="true"></i></button>

   This is how get id of pizza:


const plus = document.querySelectorAll("#plus")


     function plusQty(inc) {
            axios
                .post("/plus-qty", inc)
                .then(() => {
                    new Noty({
                        type: 'success',
                        timeout: 1000,
                        text: 'qty inc',
                        progressBar: false,
                        killer: true,
        
                    }).show();
        
                    setTimeout(() => {
                        window.location.assign("/cart");
                    }, 2000);
        
        
                })
                .catch((err) => {
                    console.log(err);
                });
        }
        
        
        plus.forEach((btn) => {
            btn.addEventListener("click", (e) => {
                let inc = btn.getAttribute("data-plus-id");
                plusQty(inc)
            //    console.log(incre)
            });
        });




 > Getting id in controller.js


       increase(req, res) {
                let cart = req.session.cart;
                let item_id = Object.keys(req.body)[0];
                let listItem = cart.items[item_id];
    
               
                // if (cart.totalQty == 0) {
                //     delete req.session.cart;
    
                //     return res.redirect("/cart");
                // }
    
                // return res.json({
                //     totalQty: req.session.cart.totalQty,
                // });
    
    
            }
    
        }

{{“user”:”61efd0ad66dc3aa50486254b”},”cart”:{“items”:{“61dc28da966c28ed6fb9e631”:{“item”:{“_id”:”61dc28da966c28ed6fb9e631″,”pizzaname”:”new peppy paneer”,”image”:”image_1641922230086_new_peppy_paneer.webp”,”price”:199,”size”:”small”,”__v”:0,”des”:”Flavorful trio of juicy paneer, crisp capsicum with spicy red paprika”},”qty”:1}},”totalQty”:1,”totalPrice”:199}}