Stick a wee hole in piece of paper. Look through it at arms length at a distant object.
Bring the paper right up to your face still looking at the object.
Now wink. Whichever eye you can still see out of is your dominant eye.
Much easier way of doing that…
Make a circle with your hands.
Put at arms length.
With both eyes open, pick something and position it in the middle, then close one of your eyes, then the other. One of your eyes will have the object appear in the middle, the other at the edge.
The side open when the object is in the middle is your dominant eye.