Push In repair collet and o-ring .25" ( 1/4" ) pn 7209566
Repair part for Sears RO ( reverse osmosis ) connections, but similar to any "quick connect" / "john guest" Fitting ( push in to lock, pull out to remove ).
See how to remove tubing,How to Use Standard and Quick Connect Fittings - Video
To remove the old "Collet", you must pull it out with needle nose pliers.
And excessive force may be required.
Then you will have access to the o-ring underneath the Collet ( in the hole ).
"Fish" it out ( small tool of any type ).
Installation is the reverse.
Put o-ring into the "hole",and then PRESS the new Collet into the hole.
It will "lock" into place.