Best way to implement proxies?

I have a request, that I know works perfectly as I've tested it multiple times, but not I want to add proxies to the request to allow multiple requests at once, my problem is Idk how to go around doing this.

I have proxies.txt file in this format:

host:port

I read this file with string[] proxies = File.ReadAllLines(location); then I split the host from the ports doing

foreach(string proxy in proxies)

string[] splitter = string.Split(':');

I'm so confused..how can I implement proxies in my requests and properly handle dead proxies and make sure every request gets done?