One way is to find out which companies are responsible for cutting down the rainforest, and to not buy their products. You can encourage other people to do the same. If their destruction of the rainforest causes them to start losing money, they might change their behaviour.
As Adam said, the first thing to do is to stop supporting companies that cut down the rainforest. The reason they are doing it is to get more money and if we stop buying their products that will not happen and they will have to stop.
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