In Mail on your Apple Watch, you can write and reply to email with a smart reply, Scribble, dictation, or emoji.
Go to the Mail app on your Apple Watch.
Scroll to the bottom of a message you’ve received in the Mail app, then tap
If you prefer to reply on your iPhone, wake your iPhone, then open the App Switcher. (On an iPhone with Face ID, swipe up from the bottom edge and pause; on an iPhone with a Home button, double-click the Home button.)
Tap the button that appears at the bottom of the screen to open the email in Mail.