If it starts to rain, stop immediately and cover the roof with a tarpaulin or visqueen sheet. Keep the roof as sheltered as possible. The decking or the resin will need to be completely dry before continuing.
If you are unable to laminate over a prepared decked before it will rain, then coat the decking with catalysed resin and cover any exposed edges. This will seal the deck and prevent moisture ingress into the deck until the laminate can be applied.
After rain stops, use cloths to soak up water, and speed up the drying process by wiping with acetone.