A good tip for ripening anything unripe (I even use it to good effect with rock-hard avocados when I'd forgotten to buy them several days before I needed them) is to put it/them in a warm place next to some ripe bananas. Or even in a plastic bag with the bananas, or in a drawer. The bananas give off ethylene gas, which sounds a bit nasty but which is actually a natural plant hormone that accelerates ripening. It works!