"Không có gì, tạm biệt!"
Translation:You are welcome, goodbye!
In context it means "you're welcome". If you're looking for a somewhat more direct translation to better understand it, it would mean "it's nothing". Kinda like "Oh no problem! It's nothing!". That phrase along with "không có chi" are the two ways I say "you're welcome" while growing up. I use "chi" when I'm being informal and "gì" when I wanna be a little more formal. Hope that helps?
You can memorise it as "there is nothing to thank for" but it doesnt sound like English phrase, so proper tralslation is you're welcome, no problem, don't mention it.
It also means nothing. When my Vietnamese wife heard it she translated it as "nothing goodbye". And then said, why would you say that? Welcome is "Cháo mứng" according to goôgle.