File Permissions for plugin?

Hello there, so i am using a plugin for my contact forms “ninja forms” and i already contacted their support, but i wanted to check if anybody else here can help me out, in short i am using a form that needs to save the form on the server “tmp” and “uploads” folder, so the plugin can e-mail me a copy of the form, the email goes through, but not the form (empty email, no attachment) because the plugin is being denied permission to “write” on the folders it needs to, so, i know you can set permissions through FTP, which i can do, but as far as i know that affects users, how can you specifi “file permissions” for plugins?