Hi Nisha,
you have to replace the “Save” button on your _NewEdit page with your own button, calling a microflow. This microflow will take the External Entity (Customers_2) as an input, you can then use the “Send external object” activity to send back the created/updated object.
Link to documentation: https://docs.mendix.com/refguide/send-external-object/
Hope this helps :)