To remove smudges using a spray cleaning gun, you shoot a high-pressure jet of cleaner at the fabric. The spray gun contains special spot removing chemicals, and once they hit the shirt, they start to break down the inks. They tend to work the best on porous fabrics such as cotton or woven polyester.
Depending on the ink you use, you may need to choose different types of spot cleaners. Some options are better for water based ink while others help to remove plastisol ink.
Troubleshooting & Repairing Spray Gun
Spray Gun - Parts List