Q: how can i find my lost iphone it is lost n its switch off so how can i find it again n my find my phone is off in setting

Hi sujit56,
 

Thank you for visiting Apple Support Communities.
 

I'm very sorry to hear that your iPhone has been lost. Find My iPhone needs to be turned on in order to track your device. I recommend using the following information from If your iPhone, iPad, or iPod touch is lost or stolen:
 

If Find My iPhone isn't enabled on your missing device

If you didn't turn on Find My iPhone before your device was lost or stolen, you can't use it to locate your device. However, you can use these steps to help protect your data:

1. Change your Apple ID password. By changing your Apple ID password you can prevent anyone from accessing your iCloud data or using other services (such as iMessage or iTunes) from your missing device.
2. Change the passwords for other internet accounts on your device. This could include email accounts, Facebook, or Twitter.
3. Report your lost or stolen device to local law enforcement. Law enforcement might request the serial number of your device. Find your device serial number.
4. Report your lost or stolen device to your wireless carrier. Your carrier can disable the account, preventing phone calls, texts, and data use.

Find My iPhone is the only way that you can track or locate a lost or missing device. If Find My iPhone isn't enabled on your device before it goes missing, there is no other Apple service that can find, track, or otherwise flag your device for you.

Best Regards.