Update fulfillment service from "custom" to "app"

[ShwetaS]

Hello Support team,

Is there a way to update a "custom" fulfillment service to "app" using APIs?

We are trying to use APIs for order fulfillments but the fulfillment service has been setup as "custom" and the APIs are failing with the error "The fulfillment service must be of api type".

Thank you for your help.