using System;
using System.Collections.Generic;
using System.Linq;
 
public class Test
{
	public static void Main()
	{
		var mainList = new List<string>
            {"Reset", "Set", "Test", "Test", "Reset", "Test", "Test"};
        var result = string
	        .Join("|", mainList)
	        //     ^ use a special character/pattern that will never use in your texts
	        .Replace("Reset", "|@|Reset")
	        //                 ^^^ use a special pattern for identifying place of `Reset`  
	        .Split(new [] { "|@|" }, StringSplitOptions.RemoveEmptyEntries)
	        // at first I split by place of `Reset` to create a list of strings that identifies by `|@|`
	        .Select(c => c.Split(new[] { "|" }, StringSplitOptions.RemoveEmptyEntries))
	        // now each string will become a list of strings
	        .ToList();
 
        foreach (var item in result)
        {
            foreach (var str in item)
            {
                Console.Write($"{str}, ");
            }
            Console.WriteLine();
        }
	}
}

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