add field in existing odoo models

cancel_reason.py

from odoo import models, fields, api, _

class SiteSurvey(models.Model):
	_inherit = "site.survey"

	cancel_reason = fields.Char("cancel reason")

	
class SiteSurveyWizard(models.TransientModel):
	_name = "site.survey.wizard"
	cancel_note = fields.Char("Cancel Reason")
	
	@api.multi
	def cancel_it(self):
		site_obj = self.env['site.survey']
		context = dict(self._context or {})
		
		for data in self:
			for srv in site_obj.browse(context.get('active_ids')):
				srv.write({'cancel_reason': data.cancel_note})
		return True
	

cancel_reason.xml

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

    <!-- view for wizard -->
    <record id="view_survey_cancel" model="ir.ui.view">
    <field name="name">account.invoice.refund.form</field>
    <field name="model">account.invoice.refund</field>
    <field name="arch" type="xml">
      <form string="Cancel Form">
          
        <field name="cance_note" />

        <footer>
            <button string='Create Cancel Note' name="cancel_it" type="object" class="btn-primary"/>
            <button string="Cancel" class="btn-default" special="cancel"/>
        </footer>
      </form>
    </field>
    
    <!-- action window -->
    <record id="action_survey_cancel" model="ir.actions.act_window">
        <field name="name">Cancel Survey</field>
        <field name="res_model">site.survey.wizard</field>
        <field name="view_type">form</field>
        <field name="view_mode">tree,form</field>
       <field name="view_id" ref="view_survey_cancel"/>
       <field name="target">new</field>
    </record>

  </data>
</odoo>
  
<!--  ADD THIS BUTTON IN YOUR XML "site.survey" VIEW -->
<button name="%(action_survey_cancel)d" type="action" string="Cancel Survey" />