Do not damage the piston ring. It is not listed in the parts fiche. The whole lower leg is sold as one unit, about $300
https://www.revzilla.com/motorcycle/ohlins-fdk100-cartridge-kit-honda-monkey-2019
https://store.hardracing.com/cart.php?target=product&product_id=35626&category_id=5433
...
https://www.youtube.com/watch?v=EwQZuG9SB-Q