Hello aci aisha,

here i give you example of modified the string supplier to owner

hope this code very helpfull for you.

<record id="purchase_order_form_view_inherit" model="ir.ui.view">
            <field name="name">purchase.order.form.view.inherit</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='partner_id']" position="attributes">
                    <attribute name="string">Owner</attribute>
                </xpath>
            </field>
        </record>

if you find this answer helpfull, please give me a thumbs up vote    

Thanks & Regards,

Ankit H Gandhi