How do you set the default DeliveryApiKey for a Content Recommendation Block?

Hello, 

I am pretty new to Episerver development, and I am working with Content Recommendations. 

Right now I am trying to make it so every new Content Recommendations block by default will have the same delivery-source (if that makes sense). 
So we have a couple of widgets set up, and I'd like the block by default to be set to "Daily News", for example. 

In the SetDefaultValues() method, I've written: 
this.DeliveryAPIKey = "Daily News"; 
(as I'm not verified yet, I am unable to upload image of my code) :(

I am aware this is not correct, but I do not understand how I set this string to one of our delivery channels.
Is there a good way of doing this?

Thank you in advance :)