If you’ve removed the brisket from the oven and it’s not fork tender, more than likely, it’s undercooked. Just pop it back in the oven. You could also slice the brisket after the allotted time and cook it for an additional 30 minutes to an hour, with the slices lying in the juices, to make it tender. Side note: Brisket becomes even more tender after it’s been refrigerated overnight in the juices, then reheated in the oven. So, don’t fret if it’s your first time making brisket and it’s not as tender as you would like. There is a way to resurrect it!