Use APKPure App
Get DuoFM FTP Plugin old version APK for Android
A Holo-styled file browser with root capabilities and split views.
Plugin for DuoFM (Duo: Holo File Manager w/ Root).
Gives access to your FTP or SSH2 (SFTP) servers.
This app should be compatible with all devices with android version 2.3.3 and up.
If it is listed as incompatible, you can try to download the apk from DuoFM web page:
http://duofm.bitbucket.org/