GitHub Docs

Converting an organization into a user

It's not possible to convert an organization into a personal user account, but you can create a new user account and transfer the organization's repositories to it.

Sign up for a new GitHub Enterprise user account.
Have the user's role changed to an owner.
Sign in (https://[hostname]/login) to the new user account.
Transfer each organization repository to the new user account.
Delete the organization.
Rename the user to the organization's name.