1. Login to your Odoo account and go to the Sales app.
2. Open any Sales Order that you want to enable margin for.
3. Click on the Edit button to edit the Sales Order.
4. Under the Order Lines section, click on the More button and select Add a custom field.
5. In the pop-up window that appears, enter "Margin" in the Field Label field and select "Float" as the Field Type.
6. Click on the Save button to create the new custom field.
7. Now, you will see the Margin field in the Order Lines section of the Sales Order. Enter the margin percentage for each product in the Margin field.
8. Odoo will automatically calculate the margin amount and display it in the Margin column.
9. Click on the Save button to save the changes to the Sales Order.

That's it! You have successfully enabled margin in Sales Order in Odoo.