“Ask the person you spoke l”h about for mechila.’
That may be assur. If no harm was done to them, you are not allowed to tell them that you spoke L”H about them. If harm was done to them, it is a machlokes, and you either have to tell them or you are not allowed to tell them (because it will make them feel bad).
Either way, you have to do the regular teshuva between man and G-d which involves: Admitting your sin, regretting it, and taking on yourself not to do so anymore.
You also have to try to undo any damage and/or do damage control. If it is possible to go back to the person whom you spoke L”H to and tell them that you were mistaken, you should do so. If you can’t actually tell them you were mistaken, at least find a way to make the L”H less bad (like by finding a “limud zchus” for the person spoken about or finding something good to say about them). Also, tell them not to send the email to anyone else or to tell anyone else what you said since you realize it may have been mistaken or inaccurate.
But first, we have to clarify that you did in speak l’H. Again, I didn’t quite get the situation?