How do I add multiple if possibilities in c#?

I'm fairly new to c# and would like help adding more if possibilites. If this doesn't make sense here is the code:

        if (flatTextBox1.Text == "XeC2YfjcEtzD6Kw7zkCssjDgoRmdZcv8")


            {
            MessageBox.Show("Enjoy Goat Hub! Credits to oreo #####");
            this.Hide();
            Form3 form3 = new Form3();
            Form3 main = form3;
            main.Show();
        }
        else
        {
            MessageBox.Show("Invalid Key or Key Copied Incorrectly");
        }

I want " if (flatTextBox1.Text == "XeC2YfjcEtzD6Kw7zkCssjDgoRmdZcv8") " to be equal to multiple things. So if a user enters any of those 2 possiblities in the text box, it will let them access form 3.