This article explains how to add patterns in Photoshop CC 2019 for Windows and Mac.
Photoshop – Save Custom Patterns for Backup and Sharing
Adobe Photoshop CC comes with several sets of patterns that work with the fill tool and layer styles, but you can also add your own patterns and save them as a custom set.
To create patterns from your own images and save them as a set, follow these steps:
Open the pattern you want to add in Photoshop and go to Select > All from the main toolbar.