First of all make sure that is is in fact a retained cap - (if it is it's not going to hurt him just to leave it until the next shed) - but there are other things that can make a snake look like he has a retained cap - like dehydration or if he has a propensity to rub his eye on things - either of which if you try to treat it as a retained cap you could end up really damaging the snakes eye.
For eye caps - take a warm wash cloth and try to hold the snakes head in it for a few minutes - except for really head shy balls this should not be a problem - they don't really seem to mind. After a couple of minutes - take the wash cloth and just gently rub the eye front to back a couple of times - you should see the eye cap come of at the front and then just peel right off. Then do the other eye.
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Tosha 
"Nihil facimus sed id bene facimus"

6.42.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Anakin Skywalker)
0.0.1 Green Tree Python (Verdi)
0.1.0 Bredls Python (Smurfette)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Desert Tortoise (Pope John Paul aka JP )
2.2.1 Fish (1,2,3,4)
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0.0.1 Lizard of unknown origin