How do you get back your data if you have acciedentaly reset your whole iphone

Plug it into iTunes and do a restore. Assuming you've been doing iTunes backups, you'll be given the option to restore from your backup.

Erase all content and settings should prompt for you to setup as new (keeps any current info), restore itunes backup or restore icloud backup. Icloud needs active wifi for hour or so. iTunes only helps if there is a backup there. PC Edit>Preferences>Devices White box will list backups present. Mac itunes>Preferences>Devices White box will list backups present.