What can be done with accidentaly oversalted beef?
Oversalting is best dealt with by serious dilution. 

I'd make a large, not very meaty dish from it, with lots of vegetables, cooked for a while. Fry onions and other veg, add liquid, and stir in the cooked beef. But soaking the meat should help as well. Either soak in plain water and discard the water, or soak in something you might add to the sauce (wine, beer, diluted citrus juice... ). I'd also cut it small before soaking/cooking. Most of the salt will be on the surface but you want to expose add much as possible of the meat to the liquid. Soaking should be done in the fridge, for a few hours.

You could go for a tomato-based sauce, a curry using coconut milk, or a sticky orange and chilli sauce, so long as the ratio of beef to everything else (and beef to initial liquid) is small. The initial liquid shouldn't bring any more salt with it, which rules out most cmmercial stock preparations, and possbile home-made stock. These are just ideas, many beef in sauce dishes would adapt. I wouldn't add more meat, but many people would.