I am not exactly sure what you require but this example may be helpful.
StringBuilder sb = new StringBuilder();
for (int i = 0; i <20; i++)
{
sb.Append($" F{i}|S{i}");
}
string testString = sb.ToString().Trim();
var names = testString.Split(' ').Select(n => n.Split('|'));
var tuples = names.Select(n => (n[0], n[1])).ToList<(string ForeName, string SurName)>();
foreach (var t in tuples)
{
Console.WriteLine($"ForeName= {t.ForeName} SurName= {t.SurName}");
}
Console.ReadLine();