How to cook the inside of a beef grilling steak?

I can cook the outside very well, but I can’t cook the inside cut. I’ve already eaten the outside and I put the inside in the fridge. How do I make it less dry and tasteless? I have a microwave , a slow cooker , frying pan and electric frying pan and an oven. I have ketchup, margarine, and not much else other than salt and pepper as condiments.