oca-mrp/odoo-bringout-oca-event-event_contact/event_contact/views/event_event_view.xml

<?xml version="1.0" ?>
<odoo>
    <record model="ir.ui.view" id="event_contacts_form_view">
        <field name="name">Event Contacts</field>
        <field name="model">event.event</field>
        <field name="inherit_id" ref="event.view_event_form" />
        <field name="arch" type="xml">
            <field name="organizer_id" position="after">
                <field name="contact_ids" widget="many2many_tags" />
            </field>
        </field>
    </record>
</odoo>