How to randomly select two strings from an array without duplicating [duplicate]

I am working on a console app that randomly selects 2 exercises from an array of exercises and uses them later in a tabata workout. I keep running into issues and the 2 selections are always the same.

Please keep your answers pretty simple as I am a beginner.

string[] tbExercises = new string[] { "Pushups", "Pullups", "Situps", "Mountain Climbers", "Burpees", "Goblet Squats", "Kettlebell Swings" };

List<string> randomExercises = new List<string>();

Random rnd1 = new Random();
string ex1 = tbExercises[rnd1.Next(0, 6)];
randomExercises.Add(ex1);
Random rnd2 = new Random();
string ex2 = tbExercises[rnd2.Next(0, 6)];
randomExercises.Add(ex2);

randomExercises.ForEach(Console.WriteLine);