The red lines mean the action that is added. First draw a line that is slightly curved

Then, add an even more curved line the opposite direction under the first one.

Split a line in the middle,

Color one side any color. Color the other side an identical color (it must be different)

Add a small slit

Color the rest black except the eye color

Add a long line across and a little one close by

Make that white

And boom! You have dragon eye.