Assuming nothing has changed since January, there are no regions for Overwatch on PS4. The game automatically does its best to connect you to the fastest client.
As for changing regions on your PS4, the short answer is you can’t. Playstion topic on region locked systems → https://www.playstation.com/en-za/get-help/help-library/store---transactions/playstation-store-information---pre-orders/why-can_t-i-change-my-country-of-residence-/