You can just download any fnf skin, for example this one:
https://skins.osuck.net/index.php?newsid=2058 , even if its up scroll. If you get an upscroll one, install it, open the skins folder (go to the skin section of the osu settings and click open current skin folder) Then find the "skin.ini" file. Double click it to open it in notepad, then scroll down to the [mania] section. Find the line that says "UpsideDown: 1" and change it to say "UpsideDown: 0". Then save the text file (ctrl+s) and reload the skin in osu! (ctrl+shift+alt+s). ^^ If anything didnt work or if u have any questions feel free to ask