i forgot my iphone passcode and i m also not able to restore it cuz it displays msg "disable find my iphone first"

You have two issues. First, to disable Find my iPhone go to https://icloud.com/find, log in with your Apple ID and password, erase the phone, then remove it from your account. You can then restore it.

If you have a recent backup of the phone either in iCloud or on your computer you can restore the backup after restoring iOS on the phone. If you don't have a backup you will lose your data.

You can disable the activation lock through iCloud (www.icloud.com). However, if you've forgotten your passcode, there's no way to access the phone again and retain the data on it. That's why you keep back ups, right?

Best of luck.