This is your best bet. Amazon usually offers both the Korean (original) and English (dubbed) versions. You can rent the HD English dub for around $3.99 or buy it for $12.99. It will stream perfectly without the risk of a takedown.
Tubi often streams Train to Busan for free. However, double-check the audio settings. Tubi frequently cycles the rights. One month they have the dub; the next month, they only have the original Korean. Look for the "Dubbed" tag in the menu. train to busan english dub youtube full
Unlike anime, where "dubs" are standard, live-action Korean films have a complicated journey to the US market. This is your best bet