If police proceeds under Section 39 of CJA 1988, based on a false allegation; then what defence I can have?

On a verbal complain of ault, Police arrests the alleged accused, takes down statement of both sides & then slaps a charge under section 39 of Criminal Justice Act, 1988 without any substantial evidence against the accused and then forces him to accept a written warning as a condition to let him off; which he accepts under duress. In such a scenario what action should be taken by the alleged accused to restore his reputation and take the complainant to task for making such false allegations.