The Control Scheme is a help menu of the various controls within Tabletop Simulator. To open up this menu in-game, press the question mark (?) key or slash (/) key. If you use a foreign keyboard, then try press the button next to ENTER or press ESC and look for Control Scheme. All of these keybinds can be changed in game in the Configuration menu.
This can be accessed by pressing the back / select button on your controller: