How do you cook grass-fed beef so it is not tough?
This is total nonsense: grass fed ribeye should absolutely not be tough. Toughness is, however, affected by the cow's breed, it's age, by how stressed it was when it was slaughtered, by ageing of the meat, and I'm sure a bunch of other variables too. Something made the meat tough, but it wasn't grass feeding - the combination of strong beefy flavour and toughness might suggest an old cow, for instance. Next time choose grass-fed beef raised by a different farmer.