What does Tu vas la repose mean in English?

"reposer" may be "poser" a second time = to put it back where it belongs, where you just taken it from: "tu vas la reposer" : [you've taken an object, and] 'you're going to put it back'

"se reposer" is 'to rest, to take a rest'

tu vas te reposer = you're going to take a rest