I recommend you to just spend that transaction. Create a new transaction using the one that is stucked and use a hight fee (enough to pay for both tx), this is called CPFP.
He can't do that because he is using Cash app, a custodial service. CPFP doesn't work in this situation because Cash App doesn't give him access to the private keys. On top of that, another centralized service (the casino Gamdom) sent the transaction, so he doesn't control the change address either.
The fees for this transaction can only be increased by Gamdom, and I don't think that's something they do. Nevertheless, it's a pretty bad estimate of Gamdom to use such low fees when they sent the transaction weeks ago.