Even though there are more than one ‘past’ tenses in nowadays English, the word ‘burst’ belongs to irregular verbs, which means you have to check the table of irregular verbs. You can easily find one online (in case you need it in future, for there is more than one irregular verb in English). I can recommend this one, check it out: https://www.englishpage.com/irregularverbs/irregularverbs.html.
It says that the Past Simple from “burst” is the same - “burst.”
If occasionally, you want to know more, there is a complex etymology behind every word, so you can easily start digging online to learn where forms and meanings come from. For instance, the irregular verb “bust’ came into modern English from Middle English (which was English language spoken after the Norman Conquest (1066) until the late 15th century) form “bersten”, which was taken from Old English (the earliest historical form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages) “ berstan”. The word “berstan” came into Old English from Proto-Germanic “brestaną” (compare West Frisian boarste, Dutch barsten, Swedish brista). The word “brestaną” in turn came from Proto-Indo-European “bʰres-” (which has the meaning “to burst,” “to break,” “to crack,” “to split,” “to separate”). This word is often compared to Irish “bris” (which has the meaning “to break”), which is considered to be an enlargement of bʰreHi (with a direct meaning “to snip” or “to split”). Also there are relations between the word “to burst” and Latin word “friare” (which is translated like “to rub” or “to crumble”), also the similarity is seen in Slovene word “briti” (with a meaning “to shave, shear”, Albanian brej (“to gnaw”), Sanskrit बृणाति (bhrīṇā́ti, “they injure, hurt”).
I hope this etymological background will give you, or understanding of the word. If you want to know more about words etymology, you can read a paper on it. Hope it helps you in studying (or it was at least interesting).