I'd start by setting aside one day to really scrub it clean. I hate cleaning with a passion, but this is one area it really helps. It's partly washing away the grime and partly washing away any bad memories and resentment. When the counters and cabinets are shiny clean - even if they are still uneven and wobbly - you'll feel like you can make a fresh start in what is now YOUR kitchen, not theirs. Put in a gel mat, get some bright and cheerful kitchen towels.
Then I'd pick one thing I really want to cook. Not a week's worth of meals, not even necessarily something healthy or productive toward my long term goals. Just something that makes me feel good. Maybe a childhood comfort food, or maybe a new curry I've been wanting to try. Build good memories.