The chart is drawn entirely from OpenStreetMap, so the way to fix the chart is to fix the map: edit in iD or JOSM, and your changes appear with the next weekly build.
The chart renders seamark:* tags plus many ordinary OSM tags (leisure=marina, waterway=fuel, leisure=slipway, natural=beach, …), so a facility mapped with everyday tagging shows up without any seamark-specific work.
- Seamark objects — the tagging reference for buoys, beacons, lights, and everything else charted.
- OpenSeaMap editing handbook — background on mapping for nautical charts.
Not sure whether something is tagged right? The viewer's inspect control (top right) toggles a debug view that shows every attribute of the feature under your cursor — the tiles carry the OSM tags verbatim.
Something tagged correctly but drawn wrong, or not drawn at all? That's a bug here, not in OSM — open an issue with a permalink to the spot.