Open your shirt mockup or canvas in Clip Studio Paint
Import the shirt design image or create the design on a new layer
Select the design layer
Use the Move tool to place the design on the shirt
Use Free Transform to resize and rotate the design
Use Mesh Transform or Liquify to match the shirt’s folds and shape
Set the design layer blending mode if needed
Adjust opacity if the design is too strong
Clip the design to a shirt area layer if necessary
Use a layer mask to hide parts outside the shirt
Add shadows and highlights on separate layers for realism
Save the file in Clip Studio format
Export the final image as PNG or JPG