Following in the methods right to input your text or artwork.

Method 1

1. Double click the Smart Object layer called “YOUR DESIGN HERE” in the layers panel.
2. Enter your text or artwork in the .psb window.
3. Close the .psb window and save the text or artwork.

or

Method 2

1. Right click the Smart Object layer called “YOUR DESIGN HERE” in the layers panel and
click the Edit Contents.
2. Enter your text or artwork in the .psb window.
3. Close the .psb window and save the text or artwork.

or

Check out the tutorial

You need to have the relevant software installed on your computer. Check the video..

Refer to this for other designs.