Add new field in "Preferences"

[gaelo]

Hello I come back in this forum to solicit assistance in development.

I want to add another field in the "Preferences" from the back office as the "

Gift-wrapping price ".

This new field should behave as the" Gift-wrapping price "and should appear at the same level as the latter.

This is to add another optional paid service to the customer order.

Thank you