The AGO has 30 short videos available on Youtube aimed for the new organist who already has keyboard skills. Here is the AGO link that provides the list of videos:
https://www.agohq.org/lessons-for-the-new-organist/

From the site: "We have created a series of 30 videos, called “Lessons for the New Organist,” to teach basic skills and techniques to beginning organists, including pianists who are making a transition to organ-playing."