Make an array of random unique numbers in a certain range

I'm working on a school project and I need to create an array (size of 30) of random unique numbers between 1 and 70.

I managed to find how to create an array of random unique numbers, but not between 1 and 70.

public int[] ShuffleArray(int[] arr)
{
    Random rand = new Random();
    int[] array = new int[70];
    for (int i = 0; i < 70; i++)
        array[i] = i + 1;
    int[] MyRandomArray = array.OrderBy(x => rand.Next(1, 71)).ToArray();
    for (int k = 0; k < arr.Length; k++)
        arr[k] = MyRandomArray[k];
    return arr;
}

I changed it based on feedback, but it still doesn't work.