Swapping back and forth using p2p/DEX/CEX but this method involves fee.
If you choose this method, make sure to swap back to a newly generated address preferably using new wallet that differs from the old one by seed, passphrase, or derivation path. Also, be sure to mask your real IP when doing so.
Centralized exchange can be used but it does not guarantee privacy. It will still be seen as a poor method to do it. If he does not want to just use coinjoin (decentralized mixer) he can use centralized mixer just as Merit.s posted already.
Yeah, providing swapping involves centralized exchange that requires KYC.
I’ve been using the non-KYC account on Huobi Global and it works fine so far. Definitely, p2p and DEXs are better for privacy, but they may sometimes lack liquidity. Their choice anyway.