It’s a two part answer…kind of. The FTP access is going to come from the i5/OS profile. So you will have to create an new profile on the System i using the CRTUSRPRF command.
Once you have that created you can go back and edit the profile so that it points it only to a certain directory in the IFS. You want to do this unless you want the user wandering all over your IFS when they FTP. So say you have a path on your IFS like
You only want that company to see the contents of the ‘CompanyXYZ’ folder and nothing else you would place that path in their user profile so that when they log in via FTP they get dropped right into that folder.
The second part is in iSeries Navigator
From the iSeries Navigator you will be able to lock down the FTP server in all kinds of ways.
All about the FTP Server on System i
Link to FTP in Navigator
It is not necessary to create a user profile for each individual just to allow FTP access. You can provide anonymous FTP to anyone. There can be significant issues with it, though; so be sure you understand what it is, how it works, and the steps needed to make it work, before trying it.
Read Configuring anonymous File Transfer Protocol and related topics for details.