Smartfit is coming soon to your Glowforge - it will be turning on for all Premium customers over the next four weeks. You don’t need to do anything - you’ll know it’s ready when you select multiple items and see the Smartfit icon.
This is a very useful tool for me! However, I have observed that Smartfit does not rotate any of the items, so if everything selected does not fit you might try manually rotating some items and then try running it again for a better fit.