Hi! You can only participate if there is a "help" symbol on a Chef's profile which can be seen in the market. The symbol is an exclamation point on the left and hand on the right. You just need to click the item to buy, once you're on chef's reataurant click cancel (since you will not buy any item) then follow the yellow arrow which will lead you to an event or to the gravespine. I hope that i was able to help.