Toytec Front coilovers clunking noise

[Herculean T4R]

My driver side Toytec BOSS coilovers is making clunking noise. It seems the shock has a loose dust cap/washer ( not sure if I'm using correct lingo) that has slid up on the shaft.

How do I fix this issue? Can I just push the dust cap back to its original place or do I need replace the shock? The coilovers are 5 yrs old w/ 35k on them.

Thanks