If you need an additional FTP user that only have access to a specific uploads folder.
Example : image designer only allowed to upload to the images folder.
First, log into your Plesk control panel and then click on
Subscriptions from the main menu
Select the domain name.
Now click on the Websites & Domains tab at the top of the page.
Click on Show More
Click on FTP Access
Select Add New FTP Account
Enter required username, and home directory for the user, password or use the Generate option.