If you specifically want the nostalgic "thuyet minh" experience from old VHS days, search YouTube first, then check the Vietnamese piracy sites as a last resort – but be very careful with your device security.
Would you like links to legal streaming services in Vietnam, or help finding subtitles instead? phim rambo 3 thuyet minh
It looks like you're looking for the Vietnamese-dubbed or "thuyết minh" version of (1988). If you specifically want the nostalgic "thuyet minh"
Here is a detailed breakdown of the movie, where to find it (legally and safely), and what to expect from the dubbed version. Plot Summary: After the events of Rambo: First Blood Part II , John Rambo has retreated to a Buddhist monastery in Thailand to find peace. His former commander, Colonel Sam Trautman, is sent on a mission to Afghanistan to help the Mujahideen fight the Soviet army. Trautman is captured by a Soviet Colonel named Zaysen. When the U.S. government refuses to help, Rambo decides to break his mentor out of a heavily fortified Soviet base in the Afghan mountains. He teams up with the Afghan rebels, using guerrilla warfare and heavy weaponry to rescue Trautman. Here is a detailed breakdown of the movie,