In short, no. Providing your phone has next-to-no coverage, a working WiFi connection, and the facility is enabled, it should work automatically - by design.
Some recent Samsung phones have an option to go "WiFi-preferred" or "mobile-preferred", toggling to "WiFi-preferred" is not generally the recommended option but may assist in testing.
Otherwise, check for the WiFi-calling indicator at the top of your phone screen when on a call, to see if VoWiFi is being used. If you have Android 15/UI7, you'll need to pull the settings menu down from the top to view this.
