I used to have money earned from usury or interest (riba), but I have spent it all and none of it remains with me. Now I want to repent. What am I required to do?
Nothing is required of you except repentance and seeking forgiveness from your Lord. Note that riba is a very serious and grave issue, seeing that Allah did not declare war in the Quran against anyone except the one who accepts riba. Since the money earned from riba has all gone, then there is nothing due from you in its regard.
And Allah knows best.