You can self sign and view and download the API documentation, but you will need to talk to a Refinitiv account manager to get a trial ID.
You can have a Refinitiv person contact you and discuss the trial details here.
PS: Can you please paste the complete link to the quickstart that is not working for you. I can access the RDP Library Quickstart just fine.
If you have signed up for an Eikon Trial or full Account, then you can create a Desktop session with the RDP library to consume streaming data from Eikon.
and then follow the C#/.NET specific sections
You will off course have to have Eikon running on the same PC where you run the C# code.