According to the wiki, in the Lite mobile edition, each Link to File field supports only one file, while the Pro mobile edition supports an unlimited number of files. I upgraded from the Lite to the Pro client so many years ago, I don't remember the one-time cost, but I don't think it was much, and it comes with some of the cloud packages, if you're using one of those.
In the Pro client, you hit the 3-line icon in the upper left corner of the entries list screen and choose Settings. The first one is File storage folder. See if you have that.