Step 1: First, open the pattern we want to customize.

Step 2: Click Edit-Define Pattern and fill in the pattern name.

Step 3: Click File-New in the menu, and click OK in the pop-up dialog box to create a new page.

Step 4: Click Edit-Fill in the pop-up dialog box, select the pattern as the filling content, click the drop-down arrow in the pattern, select the pattern as the custom pattern, and click OK to complete the filling.

Step 5: In many cases, the pattern automatically filled by the system is not what we want, so we need to modify the pattern properties.

Step 6: Double-click the background layer and change it to a normal layer.

Step 7: Double-click the layer again and click "Pattern Overlay" in the pop-up layer style.

Step 8: Click the drop-down arrow of the pattern, select our custom pattern, and control the size of the filled pattern by controlling the zoom ratio through the slider below.