I totally agree. That does not look like a retained eye-cap to me. A retained eye-cap looks dull and more opaque than it should because it has an extra layer of scales. The eye in the pic looks seriously wrinkled most likely due to dehydration.
And if it were a retained eye-cap I would never suggest that a beginner try to manually remove it. A better course of action would be to raise the humidity, possibly soak the ball, and wait till it goes into shed again. When it gets blue, start putting ointment (vaseline or triple antibiotic) directly on the eye. This wont hurt, is not invasive and does not use force (like the tape) and should help the snake have a good complete shed next time. This method is also good to use on scars.
Since you are a beginner and it has mites and dry eyes, I recommend taking it to the vet.
Laura