I think you are confusing the refusal of absolution with a penance. Canon 982 does not impose a penance of retraction and repairing the damage where a false accusing of soliciting is made against a priest. It says that absolution will be refused until the penitent does so. Under the 1741 decree of Benedict XIV,  absolution was to be refused where the confessor knows that the penitent has been solicited for sex in the confessional by another priest, and the penitent has not denounced him to the bishop or to the Inquisition. Likewise where absolution was reserved to the Pope by the same decree, a confessor would have to tell the penitent that he had no power to absolve. It has nothing to do with penance.