Prepare the cooker: spray the inside of the Instant Pot with nonstick spray or lightly oil it to prevent sticking. Alternatively, spray the slow cooker if using that method.
Place the chicken breasts in the cooker and pour the salsa evenly over the top.
If using an Instant Pot, seal the lid and cook on high pressure for 8 minutes, then perform a quick release.
If using a slow cooker, cover and cook on High for 4 hours until the chicken is fully cooked and tender.
Remove the chicken and shred with two forks or place in a stand mixer fitted with a paddle attachment and shred on low speed until pulled.
Return shredded chicken to the cooker and stir to combine with the salsa, then serve immediately or cool and store as desired.
