Array char operation C#

Question

Anyone can help me how to optimize the code that i create or have better way to implement it? The rule is on the bottom

    public string HandleLastNumber(char[] n_array)
    {
    var n_string = new StringBuilder();
    if (n_array.All(x => char.IsDigit(x)))
    {
    return $"{new string(n_array)} -> {int.Parse(n_array) + 1}";
    }
    if (!n_array.Any(x => char.IsDigit(x)))
    {
    return $"{new string(n_array)}->{new string(n_array)}";
    }
    for (int i = n_array.Length - 1; i >= 0; i--)
    {
    if (!char.IsDigit(n_array[i]))
    {
    break;
    }
    n_string.Insert(0, n_array[i]);
    }
    var n_plus = int.Parse(n_string.ToString()) + 1;
    var n_handled = n_plus.ToString()[^n_string.Length..];
    var sub_clone = new string(n_array).Substring(0,n_array.Length-n_handled.Length);
    return $"{new string(n_array)}->{sub_clone += n_handled}";
    }
    }

The rule is Input char array, validate the last number, plus one at last number. then print old and new char array
result example:

1. 00-> 01
2. 99-> 00
3. ABC123 -> ABC124
4. ABCDGF -> ABCDGF
5. AD33GVB99 -> AD33GVB00