when I go to the sheeps in (Coords: 495.983/66/290.063) they dont appear and there are only chickens and i dont know what to do.

Animals in minecraft are placed depending on the order in which the chunks around them are loaded. In order to get sheep reliably you should experiment with different render distances and make sure you run on the same path (or close to) every time

When that happens you have to reset because the chunks didnt generate in the right order, there isnt really anything you can do about it besides play on a higher view distance.