I can't offer any insight on the Excel side of things, but you can use the Dropbox API to programmatically access file data in a connected account, using /2/files/download:
https://www.dropbox.com/developers/documentation/http/documentation#files-download
(There are also corresponding methods in the SDKs, if you're using one, which we do reccomend.)
Regarding the Excel part of this, perhaps someone else on the forum has some experience with that. Otherwise, you may want to try an Office/Excel forum.