There is no command line utility for this matter.
We have 2 ways to assign agents to environment using other utilities.
- Using RA Action
You can use [Application Environment - Assign Servers] action, if you want to assign agents in your deployments.
- Using SOAP API
If you want to assign agents from external, you can use SOAP method [mapInstanceToEnvironment]. It needs some coding, so CA Services can assist you with fee if you need.