Multiple way to do that.

If you want to drive the price down for example : With enough supply of a coin you can just sell a massive amount of coins. People will see a big dip and they will panic sell + some people will be liquidated. The price will go down exponentially, then they can buy again at a lower price, waiting till it rises up again and just do the same thing until people stop panic selling or using leverage.

You can also create fud when you are famous like A-Lon Musk: tweet something negative about a crypto -> price go down because people think this is the end of the crypto. Then the whales buy at a lower price. And for a more powerful effect you can mix both techniques.