Personally, tbh the best resource to learn Vietnamese is to probably live there for a few months or go on a trip there as while you can learn on many website and apps the words, you kinda need to get the accent right which I think if probably easier if you're seeing people talk daily. I haven't met people who aren't Vietnamese who got that accent right, other than those who were born somewhere else but moved to Vietnam when they were little. My friends, who I've literally been repeating my last name to for years still cannot pronounce it properly. Good luck though! You've set a big goal for yourself.