There should be a larger diameter part that has internal threads, so it works like a nut. The smaller diameter part has external threads, so it's like a bolt, with a small through hole for the cable to go through. If the small diameter end is turned CCW, it unscrews and increases tension.
If there are not two diameters, it's not a cable adjuster. Does the frame have an adjuster?
Also see YouTube there are many videos.
Last edited by DaveSSS; 11-17-19 at 02:28 PM.