Process to Update Items with Zero Cost using FIFO

All,

We have an old 11.5.9 installation that contains numerous items that were set up improperly with a zero cost several years ago. We would like to associate a cost with all of the existing items as well as any new inventory that comes in down the road. We are using FIFO. I'm afraid that we have no in-house functional knowledge around this process and I as a developer have been asked to look into this issue. Any information that you can share on this subject would be greatly appreciated. I'm presently looking through the 11.5.9 Cost Management User's Guide, but