Does repentance have specific actions, such as prayer and charity, or is it merely heartfelt? And is there a reported supplication for repentance from sins?

A Muslim must repent to Allah Almighty from every sin. Repentance has conditions, which are: sincere remorse for committing the disobedience, abstaining from it, and resolving not to return to it.

If these conditions are met, then repentance for sins that do not involve the rights of creation is complete. It is desirable for a Muslim to frequently seek forgiveness (istighfar) and perform good deeds, so that Allah Almighty may expiate their sins thereby. Allah Almighty said: "Indeed, good deeds do away with evil deeds." And in the hadith: "And follow up a bad deed with a good deed, it will erase it."

Verbalizing the seeking of forgiveness is not a condition, but it is desirable. The prayer of repentance (Salat al-Tawbah) is desirable; it consists of two rak'ahs in which the Muslim presents their repentance to Allah Almighty. Among the supplications of the Prophet, peace and blessings be upon him, was: "O Allah, forgive me all my sins, the small and the great, the first and the last, the manifest and the hidden."