pos/pos_default_partner/views/pos_config.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2020 Creu Blanca
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<odoo>

    <record model="ir.ui.view" id="pos_config_view_form">
        <field name="name">pos.config.form (in pos_default_partner)</field>
        <field name="model">pos.config</field>
        <field name="inherit_id" ref="point_of_sale.pos_config_view_form"/>
        <field name="arch" type="xml">
            <xpath expr="//div[@id='inventory_location']" position="after">
                <h2>Customers</h2>
                <div class="row mt16 o_settings_container" id="customers_config">
                    <div class="col-12 col-lg-6 o_setting_box">
                        <div class="o_setting_right_pane">
                            <label for="default_partner_id" string="Default Customer"/>
                            <div class="text-muted">
                                Default customer to use if none is set
                            </div>
                            <div class="content-group mt16">
                                <field name="default_partner_id"/>
                            </div>
                        </div>
                    </div>
                </div>
            </xpath>
        </field>
    </record>



</odoo>