Welcome! However we are going to need some more information about your car. There are many Saturn models and they all use different transmissions.

First you need to remove the shift linkage and make sure the problem is inside the transmission. Fifth gear is under the end cover outside of the main case. You can remove the cover and take a look, it might be as simple as a shift fork needing to be replaced. It also may not have any teeth left and you need a complete rebuild. Sometimes you can just replace 5th gear components with the trans still in the car. There is an exploded view on the internet, just look up a Getrag f17 transmission. It is listed as a Vauxhall/Opel transmission since that is what your car really is.