step 1. Select your favorite style 32x32 pattern from 
https://www.textures-resource.com/gamecube/animalcrossing/texture/9187/

step 2. open your favorite image editor, such as aseprite or paint.net.

step 3 (shirt). create a 32x128 image, and copy your selected pattern 4 times.

step 4 (sleeves). same as the shirt, but only 2 times instead of 4 across a 32x64 image.