After my investigation, I noticed that this feature is currently not supported because the environment owner is determined during creation. However there is a workaround to get the ownership of existing Cloud environment by creating an EBS snapshot of the current instance and attaching it to a new Cloud9 environment.

Detailed steps are as below.

1. Context: I have an environment called Alpha in Cloud9 and I want to change the owner to user “test-cloud9-normal-user” having AdministratorAccess permission
2. Find the cloud9 instance (it is usually of format aws-cloud9-<environment_name>-XXXXXX) on EC2 console, click the link of EBS ID on Descrption tab.
3. Create a snapshot by clicking “Action”–>”Create Snapshot”.
4. Once the snapshot is created, click on the snapshot and create a volume from it. You can give that new volume a name for identification purposes.
5. Login as user “test-cloud9-normal-user” to create a Cloud9 environment by following the document https://docs.aws.amazon.com/cloud9/latest/user-guide/create-environment.html
6. After new environment created, move the EC2 console and stop that new instance
7. Find and click the link of EBS ID in this new instance.
8. Detach this volume (Action–> Detach Volume), make sure the instance is in “stopped” state.
9. Find the volume created on step 4, click Action–>Attach Volume, then choose the new EC2 instance and use “/dev/xvda” for Device. Click Attach button.
10. Open the Cloud9 console and you can see user “test-cloud9-normal-user” is the owner of new environment. By clicking Open IDE button, you will see the migrated environment.