Maybe he doesn't have to try again to access the Gamdom site but try to access other gambling sites and see if he experiences the same thing or not.
Changing DNS maybe he can try but we don't know if using that method will work properly or cause problems for him.
With so many crypto gambling sites nowadays, he should be able to choose a gambling site he can visit with no problems so that he doesn't have to try something he doesn't even know if it's good for him or brings trouble later.
At least that's what many of us advise him so he doesn't get into trouble when he wants to withdraw his money later.
Trying some sites are much easier than changing the DNS. If your not an expert at this, you will only mess up your connection and make your browser or internet unusable.
There was a thread here before about changing DNS and lets you access a blocked gambling site but that must be illegal because this can be the same as using a VPN and many gambling sites don't allow VPN. Op can try winz.io because I noticed that he carry it on his signature. He can get some coins from this site but he can return the favor by playing on this site before any other else. Winz is also accessible right now on my side. I tried gamdom and it loads perfectly too.