You would have to purchase your labels from PirateShip.com or other online shipping service. Make sure you have the buyers address as shipped from and yours as ship to.
Download the PDF of the labels to your desktop, then eMail the PDF files containing the shipping labels to your buyers. I would do this one at a time so they don’t get mixed up.
You would need to get your buyer’s eMail addresses to do that. You can get that info by calling them you can find their phone numbers in the order details under their name in the show Contact info drop down menu. I would message them first to let them know you’re calling them.
ETA: It’s always a good idea to label your orders one at a time so mix ups don’t occur.