public static void Main()
Uri requestUri = new Uri("https://arl3.api.myobdev.com/accountright-ci-r4u41/");
var map = "pub.api.myobdev.com,arl3.api.myob.com|api.myobdev.com,arl3.api.myob.com|arl3.api.myobdev.com,ci-r4u41-sea-api.dev.ar-services.myob.com|arl2.api.myobdev.com,ci-r4u41-eau-api.dev.ar-services.myob.com|arl1.api.myobdev.com,ci-r4u41-seau-api.dev.ar-services.myob.com";
var pairs = map.Split("|".ToCharArray())
.Select(x => x.Split(",".ToCharArray()))
.Select(x => new {first = x[0], second = x[1]})
var result = pairs.Aggregate(requestUri,
(current, pair) => new Uri(current.ToString().Replace("https://" + pair.first, "https://" + pair.second)));
Console.WriteLine(result);