Family sharing

You have to disband the current family and set up a new Family group with the different Organizer.

Leave Family Sharing - Apple Support --> Leave Family Sharing - Apple Support

Set up Family Sharing - Apple Support --> Set up Family Sharing - Apple Support

From: Hi, how do I make me to family organizer,… - Apple Community

"If there are children under 13 years old, the new organizer needs to leave the existing family, set up the new family, and then the under 13 years old children can be transferred to the new family. Then disband the old family and join the new family."

Move a child to another group using Family Sharing ---> Move a child to another group using Family Sharing - Apple Support

Set up Family Sharing - Apple Support

"Remember, you can only join one family at a time, and you can only switch to a different family group once per year."

Note that when doing this you may wish to set up individual bridging subscriptions to any Apple services such as iCloud and Apple Music subscriptions. If there is a time when a person who is using a subscription is no longer covered by a family plan during the transition they may lose access to features of those services, such as losing Apple Music playlists.