What should a person do who has been convicted of a forged trust receipt, and is it permissible for him to use illicit means to restore his right?

There is no harm in using lawful stratagems to ward off injustice from oneself. It is not obligatory to pay an amount ruled by the court based on a forged receipt. If the amount is paid, it is permissible to use stratagem to retrieve it, because stratagem is permissible to attain what is rightful, as in His (Allah's) saying, "Thus did We plan for Yusuf."