How can one get rid of hardness of heart and restore reverence after repentance, while preserving good deeds?

To get rid of hardness of heart, you should thank Allah for guidance, be keen on righteousness and abandoning sins, attend funerals, visit graves, contemplate death and its terrors, witness those on their deathbeds, visit the sick, and reflect on the state of those afflicted.

You should also adhere to the remembrance of Allah and frequent supplication, ponder over Allah's Names and Attributes, recite the Qur'an with reflection, seek beneficial knowledge, understand the words of Allah and His Messenger, stay away from worldly distractions, reduce excessive speech, looking, socializing, eating, and drinking, empty your heart for the Hereafter, practice asceticism in this world, accompany good people, and attend gatherings of remembrance and knowledge.