If he has already stopped betting, then let it be. That will be better for him than continuing to waste money without enjoying the bets or making a profit. 
By following prediction groups like that, the focus is clearly on making a profit. Your friend isn't really enjoying or liking those sports bets. 
If it's no longer profitable, your friend shouldn't have any reason to keep following those prediction groups and consistently placing bets based on their predictions. 
If your friend still wants to bet, it's better to use his own predictions. Just do it gradually with bets that have good chances of winning. Some prediction groups offer parlay betting solutions with big winning chances, but the risk is also high.