What is recommended to help to find dominant eye with astigmatism?

Test. Astigmatism does not affect this. Hold out your thumb at arms length using it to cover a number on a wall clock. Then close one eye and then the other. The thumb will stay over the number from the dominant eye when you close the non-dominant eye, but will jump to one side when you close the dominant eye. And which eye do you sight a telescope with? The dominant eye.