There are several ways to control the chat.
You can disable the chat altogether in the game settings by using the Disable chat from this game option.
Another option is to disable only the shoutbox. This way players can reach the game instructors using messages even though they cannot chat with each other in the shoutbox. Open the chat from the fifth button on the right. Switch off the button next to the title Shoutbox.
You can also delete individual messages from the chat. Click a message. A delete button appears next to it. Click the button. Then Confirm delete.