Is it possible to repent, reform one's heart, and rectify past corruption after committing numerous inner and outer sins and transgressions? And does Allah forgive sins if the perpetrator confesses to people what they have done in terms of backbiting and slander and asks for their forgiveness?

Sincere repentance erases all sins, and a servant should hasten to repent and not despair of Allah's mercy, for Allah rejoices at the repentance of His repentant servant. The sins mentioned do not cast their perpetrator out of the fold of Islam; even the repentance of a disbeliever is accepted. As for the intangible rights of human beings, one must seek absolution from their owners by asking for forgiveness, unless that leads to a greater harm. If harm is feared, then it suffices to supplicate for them and mention their good deeds.