Step 1: Select “Your Design”
Double click the layer “Your Design”. This opens the smart object with the designs inside.
Show the “Placement Guide” and hide layer “Replace Me”.
Step 2: Add your artwork
Place your design into the mockup by clicking File > Place Embedded.
(You can also copy-paste artwork from another Photoshop window. Just click Select > All, and then click Edit > Copy)
Position your artwork and hit enter.
Step 3: Hide “Placement Guide” + Save
Hide the placement guide, then click save. You can close the “Your Design” tab now.
That’s it! Have fun :).