Where does “vzo-” come from?

vzo- (Old Slovak) comes from Proto-Slavic vъz-, from Proto-Balto-Slavic uź — on, at; in return for.

Ancestry of “vzo-”, step by step

Step	Language	Word	Meaning
1	Proto-Slavic	vъz-	up; back
2	Proto-Balto-Slavic	uź	on, at; in return for