Hello Jignasha,

Try this :-

In .py

class EventEvent(models.Model):

     _inherit = 'event.event'

     custom_field = fields.Char('Custom')

In .xml

<record id="event_form_view_inherit" model="ir.ui.view">

    <field name="name">event.form.view.inherit</field>

    <field name="model">event.event</field>

    <field name="inherit_id" ref="event.view_event_form"/>

    <field name="arch" type="xml">  

        <xpath expr="/form/sheet/group[@name='main_field_group']/group/field[@name='date_tz']" position="after">

             <field name="custom_field"/>

         </xpath>

     </field>

</record>

From above code, your custom field display after Timezone in Event form view.

Hope it works for you.

Thanks,