That is what the licensing section is for
To add prices for licensing images, Log in as normal on pixels.com or fineartamerica.com
Either edit an image and set the prices then submit, or
Bulk edit which is in your BEHIND THE SCENES | Bulk Price edit
Set up future pricing in your BEHIND THE SCENES | Default prices
The image will then appear on licensing.pixels.com up to 24 hours later in its search or you can just send them a direct link