I grew up right handed,right eye dominant.
A 30 year carreer as a machinist caused my eyes to develop a
"skill" of the eye that can see the best takes over.If I am watching a light gap disappear or touching an end mill off,etc,depending on the setup sometimes my left eye takes over.
This became a real problem with a shotgun.All the sudden I could not hit anything!
The shotgun under my right eye caused my left eye to take over.
I talked it over with my shotgunner brother,and he told me of a British double barrel technique(I shoot a double).The left hand index finger points at the target under the forend or barrels.The left thumb points up up at the sky,on the left side of the forend.That thumb gets in the way of the left eye just enough to put the right eye back in charge.
It accomplishes the same thing as the dot on the glasses ,but it is only there when you shoot.
I wear glasses all the time,and I just cannot tolerate any tape,marker dot,smear from a Kentucky Fried Chicken bone,etc.
If that solution(tape on the glasses) works for you,great!Have fun!But please do not inflict it upon a beginner.Horrible eye strain is no fun.
Try the thumb thing,its also the natural place to ride a thumb with the 1911on top the safety,and two handed hold on a single action wheel gun,the left thumb can be up ready to thumb the hammer.
Give it a try before you say "Bah,humbug"