You should be thankful to anyone who gives you favor or goodness. And try to repay him, with the same favor or goodness. Or even, the better one.
A hadith from Jabir ibn Abdullah (may Allah blesses him), that the Prophet ﷺ said,
مَنْ صُنِعَ إِلَيْهِ مَعْرُوفٌ فَلْيُجْزِئْهُ فَإِنْ لَمْ يَجِدْ مَا يُجْزِئُهُ فَلْيُثْنِ عَلَيْهِ فَإِنَّهُ إِذَا أَثْنَى فَقَدْ شَكَرَهُ وَإِنْ كَتَمَهُ فَقَدْ كَفَرَهُ وَمَنْ تَحَلَّى بِمَا لَمْ يُعْطَ فَكَأَنَّمَا لَبِسَ ثَوْبَيْ زُورٍ
“Whoever is treated well, let him repay them. If he cannot find repayment, let him praise them for that is thanking them. If he conceals it, he was been ungrateful to them. Whoever adorns himself with what he has not been given, it is as if he wears a garment of lies” [al-Adab al-Mufrad, al-Albani says this hadith is saheeh].
If you can repay him, at least, you can pray to Allah for his goodness.
A hadith from Abdullah ibn Umar (may Allah blesses him), that the Prophet ﷺ said,
مَنْ صَنَعَ إِلَيْكُمْ مَعْرُوفًا فَكَافِئُوهُ، فَإِنْ لَمْ تَجِدُوا مَا تُكَافِئُونَهُ فَادْعُوا لَهُ حَتَّى تَرَوْا أَنَّكُمْ قَدْ كَافَأْتُمُوهُ
“anyone does you a kindness, recompense him; but if you have not the means to do so, pray for him until you feel that you have compensated him” [Abu Dawood, al Albani says this hadith is saheeh].
It is one of manners for Muslims to thank people who have helped them and repay their goodness.
Be thankful not only to humans but to Allah too. You can show it by spending your wealth to needy people at ussunnah.org/waqf