Most profitable strategy ASSUMING that you believe BTC will always come back to it's current price and you HODL until it does and don't sell otherwise

I have a friend who believes that BTC will always be back to it's current price or go higher, eventually. Let's theoretically assume that it's true. This way there's no risk for him, the money can only freeze for a while BTC price is back.

He would like me to trade for him in the most profitable way with the following conditions:

1. Never sell in loss.
   Example: Bought at the price of BTC = 50K$, only close the trade when it's BTC > 50K$
2. HODL until it does come back.
   Whether it takes weeks or months doesn't matter. He can freeze the money as long as needed.

Profit have to come from the volatility in some way. But which strategies would you use assuming that his theory is true?