The truth is you cannot edit an email once it has been sent.
Some email clients, such as Outlook and Gmail, have the feature but there is a caveat. Outlook, for example, only works within the same Outlook Exchange system. If it is sent outside of the ecosystem, it won’t work. Gmail doesn’t actually retract the sent email, but (if you have the feature turned on) will delay sending the email up to 30 seconds for you to hit the undo button.
What you can do is copy the already sent email and make the edits you need before sending it again. Best practice is to let your audience know they are receiving an updated email.