Hii @KIRAN PANWAR,
If the phone turns off when the charger is removed it appears as though the battery is failing to hold its’ charge and needs to be replaced.
Here’s a [https://www.youtube.com/watch?v=YFfJzeebKqc|video] that shows how to change the battery in the phone.
Replacement batteries are available online. Just search for ''Xiaomi Redmi Note 4 battery'' to get results for suppliers of the part.