Lay chicken into slow cooker (4 - 7 quart). Sprinkle lightly with salt and pepper (you can add more later), cumin, and garlic.
Pour in salsa verde and sprinkle in canned green chilis and Anaheim chilis. Cover and cook on low heat 4 - 5 hours or high heat 2 1/2 - 3 hours or until chicken is tender and cooked through.
Remove chicken from slow cooker (leave salsa mixture). Let rest on cutting board 5 minutes then shred.
Return to slow cooker (I ladled out 1 cup of the salsa mixture first but that's optional), toss and let rest on warm heat 10 minutes or up to 30 minutes if time allows. Toss in cilantro.
Add 1/2 cup salsa to Instant Pot, add chicken and sprinkle lightly with salt and pepper (you can add more later), and cumin, and garlic. Then pour in remaining salsa, canned green chilis and Anaheim chilies over chicken to cover.
Close lid, turn vent to "sealing" and set Instant Pot to "poultry" or "manual" setting then set to 13 minutes.
Once cycle is complete use quick release method according to manufactures instructions.
Remove chicken and let cool several minutes on cutting board then shred into pieces and (optionally ladle out 1 cup juice from the pot) return chicken to juices in instant pot, let rest on warm setting 10 minutes if time allows.
Sprinkle in cilantro, and toss chicken to coat.
Heat tortillas a skillet (as many as can fit in a single layer) in a little olive oil (or brush tortillas with oil then heat) over medium-high heat until golden brown spots appear then flip and cook opposite side. Transfer to paper towels to drain.
Lift chicken pieces with tongs from slow cooker or Instant Pot and allow excess liquid to run off, then place in tortillas in a row in the center then top with toppings (lettuce, cheese, avocado etc).
Serve immediately after assembling with lime wedges for spritzing if desired.