seitime-frappe/frappe/docs/user/guides/app_development/how-to-add-customizations-to-app.md

If you want to add Custom Fields to your app so that they are automatically created when you app is installed on a new site, you will have to add them as Fixtures in the hooks.py file of your app.

In your hooks.py file, add "Custom Fields"

fixtures = ["Custom Field"]

Export fixtures before you commit your app with:

$ bench --site mysite export-fixtures

This will create a new folder called fixtures in your app folder and a .csv or .json file will be created with the custom fields.

This file will be automatically imported when the app is installed in a new site or updated via bench update.

Note: You can also add single DocTypes like "Website Settings" as fixtures