Slide the threaded ferrule away from the end and you should see that the gold-colored insert is pressed into the end of the tube.
It pulls out but you may find it difficult to remove since it's barbed. If needed, carefully split the tubing to remove it. Heating the assembly to soften the tubing can also make removal easier.
I think it's best NOT to reuse these components as replacements are inexpensive and it's easy to have a leak with your new lines.
Here is what the parts look like:
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