https://github.com/esp8266/Arduino/pull/7941#issuecomment-810527791

wat.cpp

#include <ESP8266WiFi.h>

void setup() {
  delay(1000);
  Serial.begin(115200);
  Serial.println();
  WiFi.mode(WIFI_OFF);
}

struct Auth {
    String ssid;
    String pass;
};

Auth auths[2] {
    {"OldSSID", "OldPassword"},
    {"NewSSID", "NewPassword"}
};

void loop() {
    static auto current = std::begin(auths);

    static auto begin = std::begin(auths);
    static auto end = std::end(auths);

    static unsigned long last { millis() };
    if (millis() - last > 10000) {
        last = millis();
        WiFi.mode(WIFI_OFF);
        WiFi.softAP((*current).ssid, (*current).pass);
        delay(100);

        IPAddress myIP = WiFi.softAPIP();
        Serial.print("AP name: ");
        Serial.println((*current).ssid);
        Serial.print("AP IP address: ");
        Serial.println(myIP);

        ++current;
        if (current == end) {
            current = begin;
        }
    }

    delay(10);
}