Here's how to move him:
He's only there for a short time! This man is only blocking the entrance to the Game Corner for a specific period during the game.
Here's how to get past him:
1. Progress through the game: Continue the main storyline and advance through the game until you reach a certain point. I won't spoil it, but it's a key event in the story.
2. He'll move: After the event happens, the man blocking the Game Corner will move aside, allowing you access to the casino.
Remember: If you've already completed this event in your playthrough and the man is still there, then there might be a glitch happening. Try saving your game and restarting it.
Let me know if you have any other questions about Pokemon Silver!