This feature seems a little buried in the app. I had trouble finding it as I was clicking on individual files to try and find this feature. It seem the only way to rename a file is to open the field itself, which contains all the files. It would be nice if you could rename a file from the file viewer as well.

Is this what you are looking for? Open the file cell, then click the three horizontal dots in the top right of the file to rename the file.