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In the Kowa HighLander binoculars series, there is a black ring at the top side of the eyepieces... then there is a silver or light-colored ring (or, area) below that on both the lenses... and then there's another black ring or area below that. Where in this sequence (black, light-colored/silver, black, then the color of the main body of the binocular) did the separation of lens and binoc. occur? i.e. what of this set of rings or areas, came away?
I suspect that the clamp or other securing / tightening mechanism that held the lens in place, has slipped so that it is now too tight to re-insert the lens/lens assembly into the binocs. So you might want to find the thumbscrew or other tightening control/knob-let, and loosen it a few turns until the lens / lens assembly fits back into the binoc.
If you wish to send two pics (or two in one pic) of the separated lens/lens assly., and the place, looking into the binocs, where the lens/lens assly. went in / came out of, that would help me advise you about this problem and what best to do about it.