Do you want to change the default text/plain format emails generated by WordPress for lost password, notifications, etc… To do this you need to install this plugin below.
Go to your WordPress Dashboard, go to Plugins > Add New and type in WP Better Emails. Now select Install Now and activate the plugin. Once activated you will be able to make changes to the plugin in Settings > WP Better Emails.
Here you can first type in the name of your company or your personal name depending on what you are using WordPress for then type in your email. Ideally, you should keep it as it is unless you are comfortable with changing the code.
To view your new email template, scroll down to the bottom and you will see a box that says ‘Send an email preview to‘.
Enter your email and hit Send and you will see how the email will look in your users inbox.