If a prohibited transaction has occurred, the filer (plan administrator or employer) must take corrective action as soon as possible to remedy the situation. This may include returning any improper contributions, distributions, or other assets, and paying any required excise taxes. The filer must also file Form 5330, Return of Excise Taxes Related to Employee Benefit Plans, to report the correction. It is essential to note that correcting prohibited transactions as soon as possible can help minimize the potential tax consequences.