my iphone X battery swollen up

You need to contact Apple support: https://getsupport.apple.com. Don’t use the phone even if it works. Apple will replace the phone; if it is out of warranty and you don’t have AppleCare+ on it there will be a fee. Only Apple can tell you how much it will be.

This just happened to my iPhone X 256 gb last week. The glass totally popped up almost off the phone while in the case. Apple has sent me a box to return the phone via FEDEX (just delievered). I had to unpair my iWatch, and turn off Find my iPhone and back up and erase all content. I'm returning to Apple and they said they will replace the phone. My phone was also out of warranty. But this is a defective battery issue - no damage on my part. Google swollen iPhone. This seems to be an issue with iPhone 8 & X's - more than other models. I've had at least 4 iPhones since they were invented, and this is a first. My iPhone is like new and I'm hoping they send me a replacement in the same condition with a working battery. My phone was hot when it was being charged. I wish an Apple store had an available appointment, but there's a 1 week wait at all stores within 30 miles of my home.

Batteries are consumable parts of a device and replacing them is usually at the user's expense.

An iPhone X is well out of warranty range.