Normally you should not need to remove any lenses from an eyepiece for cleaning, since only two lenses – the eye lens closest to the eye and the field lens (at the opposite end) closest to the telescope – are exposed to dust, fingerprints, etc.
If the eye lens is accidentally removed, carefully reinsert it into position with the flattest side of the lens or lens assembly (it may be two lenses in contact – a doublet with two simple lenses attached together) outwards towards the eye.
For simple two-lens eyepiece designs it’s easy to determine which lens is oriented which way. For the Ramsden (identified by designations like SR before or after the focal length), the field lens also has its flat side out towards the scope. The Huygens type (identified as H before or after the focal length) has the flat side of the eye lens outwards and the curved surface of the field lens towards the scope.
Three-element designs are usually Kellners (K in the designation) and have two elements in contact for the eye lens and one element for the field lens. Both the eye lens doublet and the field lens have flat sides out.
Plössl eyepieces are symmetrical doublets (4 lenses) and each doublet has curved surfaces on both sides. Usually the least curved surfaces of each doublet face outwards.
Eyepieces with more elements are difficult to characterize so simply and consequently much more difficult to put back together.
Note: Disassembling an eyepiece may void its Celestron warranty.