There is an answer (from the customer service of the site I mentioned in this) that I think is quite necessary for someone who has the same thing as me. And I think this needs to be input for this site. The questions and answers that I mean are in the picture, at the link below. About welcome bonus for first deposit.
Although the bonus is not available for crypto users, their answer makes sens and it applies to all crypto casinos. The bonus will be credited to your balance automatically one you make your first deposit (it's called
first deposit bonus for a reason!).
What you can do is to send your coins from different wallets to one of your addresses then send the whole amount to the casino in one transaction.