No one can really label any adult or child as "narcissistic" or any other psychological diagnosis unless they're a professional who's seen them face to face. So I'd shy away from applying this label to your kid without it having been diagnosed properly - without it being part of a structured plan for helping them, it can too easily be a way to dehumanise them without releasing it (I know that's not what you're trying to do, it's just easy for it to happen if you're not careful about these things).
That said, the best way to deal with the situation is to put very clear boundaries in place, and then NEVER break them. Any reluctance to uphold the boundaries, and your kid will push you and test you on it - it will become a game for them.
If they're currently in a stage where they're completely out of control, I'd suggest picking 1-3 behaviours to work on (e.g. not slamming the door when they come in/out, having a set bed time, and not leaving the table until everyone has finished eating).
Before you put them in place, work out how you'll respond to temper tantrums, refusals, etc. Will there be a punishment? If so, what? And how long will it last for? Prepare yourself so you have the response you need when your child acts up. I'd even consider preparing a template statement you can say to them - e.g. "You're being unreasonable. I don't interact with unreasonable people" or whatever works for your situation.
Just focus on getting those 1-3 behaviours in place and you sticking to your boundaries about them first. This is as much practice for you - setting and maintaining clear boundaries, and managing your own stress levels when maintaining those boundaries even though your child is acting up.
After you've started getting comfortable with sticking to the rules you've laid down, and/or they're mostly complying on the first 1-3 behaviours you've been working on, then add a few more. Rinse, repeat.
It can help to break bigger routines down into smaller steps - e.g. getting up at a set time. Then getting up at a set time and brushing teeth straight away. Then getting up at set time, rushing teeth and washing face first. And so on.
Hope this helps (I don't have kids, but have looked after young relatives, trained my partner (lol!) and have a cat I've had to train with a few things, too, I've also worked with people who are genuinely diagnosed with narcissism and other personality disorders - to get them to comply, you do have to be clear on boundaries, any movement on your part, and they'll take a mile)