What can I do to fix this fireplace?

Yes, it is certainly huge and heavy looking, and as it is taking up a whole corner, it makes arranging furniture rather difficult.

Do you use the fireplace on a regular basis for heat? Do you wish to keep it in the room as a source of heat, or would you rather not have it at all?

You could reface it. Here's a link for some ideas:

https://welovefire.com/fireplaces/how-to-reface-a-fireplace/

I would consider smoothing it over and then applying shiplap or tiles in the color of your choice. I don't think you can paint directly over it because of the different surfaces. Is this gas, electric or wood burning?

Here's a post that might help https://homeguides.sfgate.com/restore-painted-brick-fireplace-35407.html

Lowes has airstone it's a stone veneer. Looks fabulous!

My suggestion would be to resurface it, here are 30 fireplaces to give you some ideas (hopefully). Just arrow to the right to see the gallery:

https://www.hgtv.com/design/remodel/interior-remodel/ways-to-refresh-your-fireplace-on-any-budget-pictures

It appears someone tried to fill it in and then went back and painted it. You could try to chip off the large areas that are filled in then paint it.

Another option would be to resurface it with wood, like shiplap.

Since the fireplace appears almost to be the focus of the room I would hire a pro and it well versed in this.

What type of decor or style are you using in that room? Modern, farmhouse, etc?

You can paint it, cover it with other stone, or remove everything, if possible, and start from scratch. It and insert set into the fireplace. It could be all stone or a wood framework with stone on the surface. If it is framework with stone on the surface it would take some work but then you can do what ever you want. I redid my fireplace, black hole in the wall, after considering all options.

https://www.hometalk.com/diy/living-room/fireplaces-mantels/fireplace-redo-15815323

My dad didn't use his fireplace (it was very bad at heating) and bought a fireplace insert and installed that.

It made a huge difference. He heated his 1800 square foot home with just that.

I think I would remove the stone, It will be a tedious and very messy job, but in the long run will look much better. You could then go to Floor and Decor or any other stone store and buy stone of your choice. Of course you will have to reframe the area, but it will be much more sleek.

I’d clean it up well and give it a fresh coat of paint.