If you are using the developer dashboard you will first need to switch to the Classic UI. If you see a Developer prompt in the top left, click it and select Classic UI to switch to the Classic UI.
Sign up for an Okta developer account.
In your Okta account (make sure you are signed in as an admin), use the App Wizard to build a Single Sign-on integration with Okta.
When you are ready, navigate to the Feedback tab of the App Wizard:
Once submitted, you can track the stage of your integration in the OIN Manager.
Note: Okta doesn't proactively add SWA-only, branded apps to the OIN. If you want a branded app in the OIN that only supports SWA to all customers, submit a request to firstname.lastname@example.org.