how to pass validation error message to another page?

I have a form under user controller

And i have another controller call my_account,

i render the _form inside the index page of my_account. to allow user
to update their user information.

So when user click update, update method in UserController will be

My question is, if faild to update user object, how can i display
error message on to my_account index page, and still have the field
highlight?? e.g invalid format of email address

    -- new.html.erb
    -- _form

    -- index.html.erb