Translation:It is on the bottom left.
あります／います are used to say that something exists,. "Thing exists at this place" is how you say where something is in Japanese (in my experience anyway - definitely on Duo!)
です is used for describing things, their state. In a lot of languages that would include their location ("thing is over there"), but that property just happens to be phrased in terms of existence in Japanese
あります is an existence verb, also used to say where something is, so I think an accurate translation would need a sense of "there's a thing and it's located at the bottom left". "It's bottom left" could be more describing a thing, maybe pointing something out ("the thing I'm talking about is the bottom left one") so that would imply です? Maybe it would be read as a direction instead of a position!
It's subtle (and I definitely don't know enough to say if it's wrong!) but I think being explicit about location is safer. Especially on Duo, it wants to make sure you understand the difference between verbs