Tableau cannot connect directly to a file on an FTP server.
Unless you can map the SFTP location as a network drive or something similar, you won't be able to do this. I believe you used to be able to do that in Windows XP or similar but I haven't tried in years.
You're probably going to need to create a process to transfer the files to a local drive or network drive (this is simple, there are a lot of apps and online tools available for this)
thanks i have solved the issue using java script