Trim and cut the chicken breasts into bite-sized pieces and season with the garlic powder, cumin, chili powder, and salt.
Add the seasoned chicken, frozen sweet corn, sour cream, and mayonnaise to the slow cooker; stir until evenly combined.
Cover and cook on high for 2 to 2.5 hours or on low for 2.5 to 3 hours, until the chicken is cooked through.
Place the cream cheese on top of the hot chicken mixture and cover for 5 to 10 minutes to soften the cream cheese.
Stir the softened cream cheese into the chicken mixture until smooth and evenly combined.
Top with crumbled queso fresco and chopped cilantro; optionally sprinkle with Tajín before serving.