how can reset my lost phone?

Unless you had Settings > iCloud > Find My iPhone enabled on it then there isn't any way to try and locate it and/or remotely wipe it. If you did have it enabled then you could try locating it either via http://www.icloud.com on a computer or Find iPhone app on another iOS device - but that will only work if it's connected to a network and Find My iPhone hasn't been disabled on it.

If you think that it was stolen then you should report it to the police. You should also change your iTunes account password, your email account passwords, and any passwords that you'd stored on websites/emails/notes etc., and contact your carrier.

if you activated the find my iPhone feature then you can do it by logging into www.icloud.com and use the find my iPhone feature

if you did not you can't but they can't get by your passcode to access your information without restoring it to factory settings which would clear your information