Hypothetically, to reverse the act of ringing, or the consequences of the action.
In a criminal trial, if the prosecution brings in inadmissible evidence that would unfairly prejudice the accused, a mistrial may be warranted. Having the judge admonish the jury to disregard the evidence might not be enough, as the saying goes, 'You can't unring the bell.'
Her lofty song commands in thrilling strains That new-raised woman snap her rusty chains, Unring her finger and unbind her breast.1979, John Jefferson Bray, “The Story of Iphis”, in Poems 1972-1979: