how to make cook tuna?

You can pan fry, grill (BBQ), or bake tuna. I think the grilling method is best for tuna. he current trend is (has been) to cook tuna to about medium-rare to medium and certainly not well done.

When grilling lightly coat (paint it on) the meat with oil and season with salt & pepper. Grill on each side approximately 2-3 minutes depending on heat and other variables. I often used a compound butter on tune like a roasted garlic and herb butter and a hint of white wine reduction.

The best tuna dish I ever made was a deconstructed tuna casserole. It was black fettucine, topped with homemade mushroom cream sauce, a couple steamed veggies, I can't remember what, just use what you like, and finished with a perfect hunk of pepper encrusted pan seared tuna. Just a minute of heat on each side is what you want, its best still bright pink in the center, but like steak, people have their preferences and it's still good medium or medium well. Imho, well done is too much.

All you need to do is to put it onto a plate or into a pan and heat

Dune