If someone violated the laws against speaking Rechilut, and he wants to
repent ("do teshuva"), he has not even achieved partial repentance until
he requests forgiveness from and appeases the person he wronged. In the
case of Rechilut, this would be the subject of the Rechilut, the person
spoken about, since the talk encouraged the listener's animosity against
the subject. He should also repent for violating the commandment "Lo
telech rachil b'ameicha," do not go about as a talebearer among your
people, by repenting to G-d.
In Hilchot L"H 4:12 and the footnotes there, the Chafetz Chaim mentions
the possibility that the sinner may not be allowed to ask forgiveness of
the person he wronged. If the person who was spoken about does not know
what was said about him, or doesn't know anything was said about him, it
would cause that person anguish to hear about it, which is a violation of
"Lo telech rachil b'ameicha" (Lev 19), the commandment not to speak Lashon
Hara or Rechilut. This is frightening, as it means that in many cases
there may be no repentance for Rechilut.
I heard it suggested that it may be permissible to tell the person "I
said something about you," and ask forgiveness on that basis, but it
would depend upon how the person would react to the information. A Rabbi
knowledgeable in the laws of proper speech should be consulted.
In any case, the speaker should go back to all the parties he spoke to,
and retract what he said. This may mean finding a reasonable explanation
for what happened rather than the more slanderous interpretation offered
originally, or explaining that the speaker didn't know what he was talking
about (it was a rumor, he didn't witness it and there were other
The Chafetz Chaim likens speaking L"H to ripping open a feather pillow in
the wind - the feathers spread so quickly it is nearly impossible to
recollect them all. And the longer one waits to retract what he said,
the more the information spreads and the more damage is inflicted on the
subject of the Rechilut or L"H.