Why my phone is restart automatically?

Hi @rudrakshisharma

Try using the phone in safe mode and check if it works OK.

If it does then a downloaded app¹ is the cause of the problem. The trick is to find out which one.

You will need to uninstall each downloaded app, one by one and test the phone in normal mode to check if it now works OK. When it does then the last downloaded app that was uninstalled, was the culprit.

¹ A downloaded app is one that you downloaded and installed on the phone and wasn't one that was already installed on the phone when you first got it.