Have to installed trial version Orchestrator 2018.4.3 for you and tried to add robot option but failed to do so?
In this case, you just do not use the trial version. Better if you use the Community edition. This will allow you to add robot to demo orchestrator in UiPath.4.
The good news is that Orchestrator Community Edition is free of charges and license. You get the licenses right after you provision your environment.
Use https://platform.uipath.com/ URL and create your work environment. Here you can find the latest version of the orchestrator. Don’t register your device with any enterprise and the edition will work.