How do I load URL in iframe using an array value?

How do I use an array value (...i.e. myList(2) ...) instead of a hard coded url in the "Parameters for iFrame: navigate to url" dialogue pop-up?

Currently if I place in a YouTube url like so "https://www.youtube.com/embed/ZPG1t-gZfds" it works fine but in my array, I have 15 url values like so:

myList (0) = youtube.com/embed/video1

myList (1) = youtube.com/embed/video2

myList (2) = youtube.com/embed/video3

When I try a variable or an array value I get a server error in the iframe: "Server Error in '/' Application.

Runtime Error..."

Thank you in advance. Cheers.