Hi,

In order to create a mobile app for odoo, you have should have knowledge in the mobile app development and any of related languages like andriod, ios or flutter.

If you are good in any of mobile app language and looking how to fetch or update data from/to odoo, you can use odoo external api: https://www.odoo.com/documentation/16.0/developer/reference/external_api.html

Also for mobile app development in odoo, see: Odoo Mobile App Development

Thans