When it comes to tawba, or repentence, the most important point is that its door is always open. It can be done with any words or expressions, and its only real condition is sidq, or sincerity. The sincere repentence will naturally comprise of four parts:
1 admitting what we've done
3 asking Allah's forgiveness
4 committing never to do it again
Of these four, the most important is regret. The Prophet ﷺ said, "The [essence of] tawba is regret."
Even if a person has an addiction, they may repent, with the intention that they will not willingly return to it. Addicts have one cardinal rule in their journey to purification: never giving up.
Tawba can be expressed by any means and any words, most popularly, "astaghfirullah."
A man once said, "O Allah your forgiveness is wider than my sins, and I have more hope in your mercy than in my actions." He repeated this three times, then the Messenger ﷺ said, "This man has been forgiven."
The dua of Prophet Yunus is among the greatest prayers of repentence since it contains tawhid, tanzih, and tawba.
"There is none worthy of worship but You; glory be to You; I was from the wrong doers."
INNI KUNTU MIN AL-DHALIMEEN.
Because tawba simply means turning back to Allah, every type of believer makes tawba, even those who cannot think of what sin they committed. They turn back to Allah from not remembering Him, to remembering Him. Or from having light focus to having strong focus. The Messenger ﷺ himself used to seek forgiveness over seventy times a day.
When tawba enters the heart of the believer, punishment flees.