Allah subhana wa-ta'Ala's mercy surpasses his wrath (1), and the way to gain this mercy is to ask for forgiveness. Remember Adam Alay-hi ’s-salām's dua:
رَبَّنَا ظَلَمْنَا أَنْفُسَنَا وَإِنْ لَمْ تَغْفِرْ لَنَا وَتَرْحَمْنَا لَنَكُونَنَّ مِنَ الْخَاسِرِينَ
“Our Lord, we have wronged ourselves, and if You do not forgive us and have mercy upon us, we will surely be among the losers.”
— Surah Al A’raf verse 23
It sounds like you genuinely regret your actions which is part of repentance:
Abdullah ibn Mas’ud reported: The Messenger of Allah, peace and blessings be upon him, said, “Regret is part of repentance.”
Source: Sunan Ibn Mājah 4252
Grade: Sahih (authentic) according to Al-Albani
Further the fact you went back to find their car, shows you have put in the extra effort required to follow through on making good in your bad deed. There is a hadith that I think covers a similar situation (except from before a calamity strikes, not after):
Anas ibn Malik reported: A man said, “O Messenger of Allah, should I tie my camel and trust in Allah, or should I leave her untied and trust in Allah?” The Prophet, peace and blessings be upon him, said, “Tie her and trust in Allah.”
Source: Sunan al-Tirmidhī 2517
Grade: Hasan (fair) according to Al-Albani
By returning back, I believe you have done the same as the man tying the camel. You might rely on Allah subhana wa-ta'Ala for forgiveness but you also went to right the wrong you committed.
If Allah had wanted you would have found the car's owner. Had Allah decreed against it you could have never found them despite searching for your entire life. And verily is our entire life in the hands of Allah!
The fact you have been spared having to apologize in person and pay for the damage could well be a blessing from Allah subhana wa-ta'Ala (although I won't go as for as to say that it must be, only Allah knows for sure.)
And perhaps the accidental damage to the car somehow benefits the owner. For example, there is the example of al-Khadir damaging the boats in Surah al-Kahf, to prevent their theft.
Only Allah knows what will happen on the day of judgement, but perhaps insha'Allah you will be shielded from the car owner's anger because of the good steps you took to undo the damage, or some hidden blessing for them that was in that incident.
Continue seeking forgiveness from Allah and ask from Allah that the car owner forgives you — do not worry too much about the car owner themself, now that you have looked for them, and focus on asking Allah for forgiveness.
- Ṣaḥīḥ al-Bukhārī 3194, Ṣaḥīḥ Muslim 2751