Bison is "the best Beef"...In that - nutritionally it is fantastic, most like eating salmon. But you are correct...there is less fat.
When you have cuts of red meats ( including game ) that are lower in fats - there are a couple of things you can do that assist you.
1. add some fat. NOT olive oil because olive oil - while very healthy at room temp. and low temps - loses it's healthy food status when we turn up the heat on it- actually becoming an "oxidant" ( no longer and anti-oxidant). Use a high smoke point oil or fat such as avocado oil - or even small amount of butter.
2. Think about cooking this meat a a lower temp for a longer period of time. Then sear it. Sure - you can reverse the order of this.
3. For the ultimate in tenderness - vacuum bag it and cook it Sous Vide. You can sear it before or after this. You may also like it if you cold smoke it for 1-2 hours first....then sear, cool down - vacuum bag and Sous Vide.
The most tender, flavorful and expensive steak you will EVER eat...will be one cooked via Sous Vide, then finished on a steaming hot grill for 1 minute on each side.