II deleted my complete email on my iPhone by mistake how can I get that back with all my mail

Swipe your home screens all the way to the left to get to the App Library. From there, find the Mail app and you can press and hold, then drag the app to a home screen. From there, you will have to add each of the mail accounts you want back on your device. If these are IMAP accounts, once you add the account back, the mail will sync back to your device.

See this for how to add mail accounts. Add an email account to your iPhone, iPad, or iPod touch - Apple Support