You've cooked that tongue. Now what are you going to do with it?
Beef tongue au naturel is quite good. You don't have to make a sauce. You can serve it as is with rice, potatoes or pasta and any veggies you like. Below are pictures of a few things I've done, but let that not limit you in any way. Improvise, give your imagination free rein.
Pic4: in a cold salad
The majority of beef tongue sauces I have seen are tomato-based.
Again, these are just a few possibilities of many. If you have a sauce recipe that you like, try t with beef tongue. It will most likely be great.
Pic10: tomato sauce
Pic13: Aurora sauce