HI,

If it is needed in your custom module, you can directly add the new buttons in the header of the form as follows:

See: https://ibb.co/Wsy6Gny

Also you can control the button visibility based on the state of based on the user group. 

Then you have to define a function, that will get executed on clicking the button,

def action_confirm(self):
    self.state = 'confirm'

Thanks

Hi,

Try add the button code on xml to get a button view in needed form.

< form>
  < header>
    < button name="get_approval" string="Approval" type="object" class="oe_highlight"/>
  < /header>
< /form>

and just add the function in the .py file for changing state in the button click,

def get_approval(self):      
 self.state = 'changing_state'

You can also refer the following apps for approval purpose.

https://apps.odoo.com/apps/modules/13.0/account_payment_approval/

https://apps.odoo.com/apps/modules/13.0/invoice_multi_approval/

If you are using an enterprise edition then you have the option to configure the approvals using the studio module.

https://www.odoo.com/event/odoo-experience-2020-2622/track/studio-approvals-and-workflows-3908

Regards