suite/helpdesk_rma/views/helpdesk_views.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <!-- Helpdesk Ticket -->
    <record id="helpdesk_ticket_view_form_inherit" model="ir.ui.view">
        <field name="name">helpdesk.ticket.form.inherit</field>
        <field name="model">helpdesk.ticket</field>
        <field name="inherit_id" ref="helpdesk.helpdesk_ticket_view_form" />
        <field name="arch" type="xml">
            <xpath expr="//button[@name='action_open_helpdesk_ticket']" position="after">
                <button class="oe_stat_button" type="object" name="action_partner_rma"
                        context="{'search_default_partner_id': partner_id, 'default_partner_id': partner_id}"
                        attrs="{'invisible': [('partner_id', '=', False)]}"
                        icon="fa-cubes">
                    <field string="RMAs" name="rma_count" widget="statinfo"/>
                </button>
            </xpath>
        </field>
    </record>

</odoo>