Before eating something, you must say at least “Bismillah”. (Bukhari, Hadith: 5376). There is another dua before eating you should say.
It would be best if you recited this dua before eating:
بِسْمِ اللهِ وَبَرَكَةِ اللهِ
Bismillāhi Wa Barakatillāh
Meaning: (I start eating) In the name of Allah and upon Allah’s barakah (blessings).
– Mustadrak Al-Hakim 4/107; Shu’abul Iman Baihaqi, Hadith: 4604
If you forget to say “Bismillah” before eating, you must say:
بِسْمِ اللهِ أَوَّلَهُ وَآخِرَهُ
Bismillahi Awwalahu Wa Akhirahu
Meaning: In the name of Allah in the beginning and the end.
– Abu Daud, Hadith: 3767; Tirmidhi, Hadith: 1858