If a person commits Zina, is this forgivable? If so, then how is forgiveness attained?
You can't fix what has happened already. So, stop trying to fix it and start repenting for your sins. Allah says (what means):
Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah . Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful." [Quran 39:53]
Good deeds efface bad deeds, so try to do more good deeds (e.g. charity, prayer, fast) to efface your sins.
Ibn Mas'ud (May Allah be pleased with him) reported:
A man kissed a woman. So he came to the Messenger of Allah (ﷺ) and informed him about it. Then Allah revealed this Ayah: "And perform the Salat, between the two ends of the day and in some hours of the night. Verily, the good deeds efface the evil deeds (i.e., minor sins)." (11:114) The man asked the Messenger of Allah (ﷺ) whether this applies to him only. The Messenger of Allah (ﷺ) said, "It applies to all of my Ummah."
[Al-Bukhari and Muslim].