Can i Replace my phone battery in free of cost on apple store

No. You have a phone which was released in 2017, over 5 years ago. The battery health has degraded to the point the battery needs to be replaced. But it will NOT be replaced for free.

Based on this link you'll have to pay Apple $69 to replace the battery in your iPhone X --> iPhone Battery Repair & Replacement - Apple Support

Note: This is in the US. If you are outside the US, your cost may be different.

If you are within the warranty period or have Applecare plus, probably.

Since it's an iPhone X, discontinued 4 years ago, you will have to pay.

I need my phone battery to back to the normal