Actually it depends on the target of your friend. If he plans to keep it a long time, then he doesn't need to do anything unless to keep holding until the price can be above $19,000. The problem is when your friend needs urgent money in a big amount, so he should sell the Bitcoin at any price. But, if he has enough money and not needed to sell the Bitcoin, I suggest HODL strategy. Of course, it is not easy to hold Bitcoin for a long time, it needs a strong belief and a calm mind. However, if you trust in Bitcoin, you won't doubt it to keep a long time.
That is the time that your friend accepted the losses he got from bitcoin. Because basically if you bought at that high amount, you should keep your bitcoin and hodl it for a long time, wait for the price to be equal or somehow increase a little bit so you can compensate the time of your waiting for a small profits. But for us who believe in the capability of bitcoin, there's always a chance that we can reach ATH because of the mechanism of halving which pushes demands for bitcoin's price to increase. Wait, they are really pushing the price because miners need it. And I think everyone wants bitcoin's price to increase so it's not impossible for these investors to still have profits soon, in the long run, so just wait.