pms/pms_crm/views/pms_property.xml

<odoo>

    <record id="view_pms_property_form" model="ir.ui.view">
        <field name="name">pms.property.form</field>
        <field name="model">pms.property</field>
        <field name="inherit_id" ref="pms_base.view_pms_property_form" />
        <field name="arch" type="xml">
            <xpath expr="//div[@name='button_box']" position="inside">
                <button
                    name="action_view_leads"
                    type="object"
                    class="oe_stat_button"
                    icon="fa-pencil-square-o"
                >
                    <field name="lead_count" widget="statinfo" string="Leads" />
                </button>
            </xpath>
        </field>
    </record>

</odoo>