What’s the smartest way to slowly get rid of a large amount crypto, without affecting the market?

Lets say, hypothetically, a close friend put $15,000 into a project back in march 2020 and is now wanting to take out 90% of profits, without significantly shaking up the market.

This project has now reached $3.40 and he now has enough money to let him live comfortably for the rest of his life. How does he go about it the most efficient & effective way?

Let’s assume, hypothetically, he distrusts lawyers/central exchanges. What would be the smartest way to move funds without attracting unnecessary attention or affecting the price?

Let’s say his goal is have 90% in his bank account as fiat (and pay the relevant taxes of course), so that he can finally live like a rich person & slowly filter back into crypto once his life is sorted.

What is the best move, hypothetically speaking?

Edit: Rip my inbox.

Edit2: its hilarious how many scammers have messaged me after this post. Binance support, KuCoin services, lol, just lol.