You can either:
- Open an issue on the Drupal.org project ownership queue, asking to make the new project owner a user on drupal.org that you know be willing to become the new project owner
- Open an issue on the same queue, asking to make the new project owner the maintainer who did more commits or who was more active in following and answering the project issues
- Open an issue in the same queue, stating you are seeking for a new project owner, using Needs maintainers as Component value
Once you open the issue queue, the procedure will be handled by Drupal.org site moderators.
As alternative, you could simply set the Maintenance status field of the project to Seeking new maintainer and (eventually) the Development status to No further development. Users who need the project, and who are able to develop code for a project, seeing you set that status, could ask to be the new project owner or maintainer, if they are interested.
Finally, if you think you won't maintain anymore a project hosted on drupal.org and you won't use Drupal, you could delete your account on drupal.org. Authenticated user are now able to delete their account on drupal.org, for any reason they could have.