and after that he finally got interested in investing in Bitcoin, and downloaded the exchange app and he immediately ask to be guided by me to buy bitcoin, and to be honest I'm happy because my neighbors invest in bitcoin just like me..
Hope after buying bitcoin from exchange, you adviced him to transfer the bitcoin to a non custodial wallet, he shouldn't leave his bitcoin on exchange, we all saw what have been happening to some crypto exchange recently, no exchange is safe so if you leave your bitcoin on exchange, then the bitcoin those not belong to you completely.
You should make sure you enlighten the user about wallet security, you should tell him the best wallet to secure bitcoin, how to protect the wallet, how to secure the wallet private key. Private key should be stored in a place were their is no internet connection, it should be stored completely offline.