Synthetic rattan needs no seasonal treatment. Every 2-4 weeks wipe the weave with a soft damp cloth and a drop of neutral soap.
Avoid abrasives and solvents - they can mark the surface. After rain, let the furniture air-dry.
Store cushions in covers or move them somewhere dry for winter. The aluminium frame won't rust - just check fixings now and then.
If the weave is damaged we repair pieces and match the same profile shade.