Sure, the code is below.
As this code is part of a GitHub-repository, the most recent version can be found here:
GitHub - NorthyIE/DasKit-C7BB-Tuning: Tuning the C7BB display using an ESP32 (in the "WiFi-AP"-folder).
The password is just temporary, as this is a public project. The final code running on my ESP will have a different SSID and password, but thanks for the reminder 
// Import libraries
#include <WiFi.h>
#include <Arduino.h>
#include <ESPAsyncWebServer.h>
#include <SPIFFS.h>
// WiFi-AP SSID & Password
const char* ssid = "Moscow Plus";
const char* password = "Moscow1234";
// IP-Configuration
IPAddress local_ip(192, 168, 1, 1);
IPAddress gateway(192, 168, 1, 1);
IPAddress subnet(255, 255, 255, 0);
AsyncWebServer server(80);
// Stores the current states, disables tuning on boot
String tuningState = "AUS";
// Tuning-specific
const byte numBytes = 32;
byte receivedBytes1[numBytes];
byte numReceived1 = 0;
byte receivedBytes2[numBytes];
byte numReceived2 = 0;
boolean newData1 = false;
boolean newData2 = false;
byte sendBytes[numBytes];
void notFound(AsyncWebServerRequest *request) {
request->send(404, "text/plain", "Nothing here..");
}
void setup() {
// Serial configuration
Serial.begin(115200); // USB-Serial console
Serial1.begin(9600, SERIAL_8N1, 12, 13); // Additional consoles for display and controller communication
Serial2.begin(9600, SERIAL_8N1, 14, 15);
// Starting WiFi-AP
if (!SPIFFS.begin()) {
Serial.println("An Error has occurred while mounting SPIFFS");
return;
}
WiFi.softAP(ssid, password);
WiFi.softAPConfig(local_ip, gateway, subnet);
server.begin();
// Show on console when booted
Serial.println("-= NCM Moscow Plus Controller ready =-");
Serial.println(" -= WiFi-AP & HTTP server started =-");
server.on("/", HTTP_GET, [](AsyncWebServerRequest * request) {
if (tuningState == "AN") {
request->send(SPIFFS, "/tuningan.html", "text/html");
}
else {
request->send(SPIFFS, "/tuningaus.html", "text/html");
}
});
server.on("/tuningan", HTTP_GET, [](AsyncWebServerRequest * request) {
tuningState = "AN";
Serial.println("Tuning enabled");
request->redirect("/");
});
server.on("/tuningaus", HTTP_GET, [](AsyncWebServerRequest * request) {
tuningState = "AUS";
Serial.println("Tuning disabled");
request->redirect("/");
});
server.on("/style.css", HTTP_GET, [](AsyncWebServerRequest * request) {
request->send(SPIFFS, "/style.css", "text/css");
});
server.onNotFound(notFound);
server.begin();
}
void recvBytesWithStartEndMarkers1() {
static boolean recvInProgress = false;
static byte ndx = 0;
byte startMarker = 0x3A; //muss mit 0x3A beginnen
byte endMarker1 = 0x0D;
byte endMarker2 = 0x0A; // und mit CR LF enden
byte rb;
while (Serial1.available() > 0 && newData1 == false) {
rb = Serial1.read();
if (recvInProgress == true) {
if ((rb != endMarker2) || (receivedBytes1[ndx - 1] != endMarker1)) {
receivedBytes1[ndx] = rb;
ndx++;
if (ndx >= numBytes) {
ndx = numBytes - 1;
}
}
else {
receivedBytes1[ndx - 1] = '\0'; // terminate the string
recvInProgress = false;
numReceived1 = ndx - 1; // save the number for use when printing
ndx = 0;
newData1 = true;
}
}
else if (rb == startMarker) {
recvInProgress = true;
}
}
}
void recvBytesWithStartEndMarkers2() {
static boolean recvInProgress = false;
static byte ndx = 0;
byte startMarker = 0x3A; //muss mit 0x3A beginnen
byte endMarker1 = 0x0D;
byte endMarker2 = 0x0A; // und mit CR LF enden
byte rb;
while (Serial2.available() > 0 && newData2 == false) {
rb = Serial2.read();
if (recvInProgress == true) {
if ((rb != endMarker2) || (receivedBytes2[ndx - 1] != endMarker1)) {
receivedBytes2[ndx] = rb;
ndx++;
if (ndx >= numBytes) {
ndx = numBytes - 1;
}
}
else {
receivedBytes2[ndx - 1] = '\0'; // terminate the string
recvInProgress = false;
numReceived2 = ndx - 1; // save the number for use when printing
ndx = 0;
newData2 = true;
}
}
else if (rb == startMarker) {
recvInProgress = true;
}
}
}
void modNewData() {
sendBytes[0] = 0x3A; // neues Telegramm mit 0x3A beginnen
for (byte n = 0; n < numReceived1; n++) {
sendBytes[n + 1] = receivedBytes1[n]; // Die empfangenen Bytes an die nächsten Positionen
}
sendBytes[10] = 0x0D; // CR und LF ans Ende
sendBytes[11] = 0x0A;
if (tuningState == "AN") { // Nur, wenn Tuning via Web-Gui aktiviert ist!!
if (sendBytes[3] == (0x42) ) { // Wenn das 4. Byte 0x42 (2. Stufe) dann
sendBytes[2] = (0x0B); // 3. Byte (Unterstützungslevel)
sendBytes[3] = (0x46); // 4. Byte (Stufe) auf 6
sendBytes[4] = (0x24); // und 5. Byte (Speed) auf 36km/h
}
}
}
void Checksumm() {
sendBytes[8] = 0;
for (byte n = 1; n < 8; n++) {
sendBytes[8] = sendBytes[8] + sendBytes[n];
}
}
void showNewData() {
if (newData1 == true) {
Serial.print("received: ");
for (byte n = 0; n < numReceived1; n++) {
Serial.print(receivedBytes1[n], HEX);
Serial.print(' ');
}
Serial.println();
Serial.print("mod: ");
for (byte n = 0; n < 12; n++) {
Serial.print(sendBytes[n], HEX);
Serial.print(' ');
}
Serial.println(); // bis hier DebugInfo via USB an PC
Serial1.write(sendBytes, 12); // Telegramm rausschicken
newData1 = false;
}
if (newData2 == true) {
Serial.print("receivedMotorC: ");
for (byte n = 0; n < numReceived2; n++) {
Serial.print(receivedBytes2[n], HEX);
Serial.print(' ');
}
Serial.println();
newData2 = false;
Serial.println(); // bis hier DebugInfo via USB an PC
}
}
// Tuning-Loop
void tuning() {
recvBytesWithStartEndMarkers1(); // Checks for new message from display
modNewData(); // Does the magic
Checksumm(); // Calculates the checksum
showNewData(); // Sends modified data
recvBytesWithStartEndMarkers2(); // Checks for new message from controller
}
void loop() {
tuning();
}