In Odoo 13, you can add the option to adjust the quantity of products purchased in a popover by customizing the JavaScript and XML code. Here’s a basic example of how you might do this:

1. JavaScript Code: Extend the 'ProductConfiguratorMixin' to add the 'onClickAdd' and 'onClickRemove' methods:

odoo.define('your_module.product_configurator', function (require) {

    "use strict";

    var ProductConfiguratorMixin = require('sale.ProductConfiguratorMixin');

    ProductConfiguratorMixin.include({

        events: _.extend({}, ProductConfiguratorMixin.prototype.events, {

            'click .o_add': '_onClickAdd',

            'click .o_remove': '_onClickRemove',

        }),

        _onClickAdd: function (event) {

            // Your logic to add a product

        },

        _onClickRemove: function (event) {

            // Your logic to remove a product

        },

    });

});

2. XML Code: Add the + and - button

https://pastebin.com/jsq5GSZp

In this example, the + button calls the '_onClickAdd' method and the - button calls the '_onClickRemove' method when clicked. You should replace 'your_module.product_configurator' and other placeholders with your actual data and add your own logic to add and remove products.

Hope this helps.

Best regards,
Maciej Burzymowski