Sending AT Commands

I Managed to solve it.
My final code is the following:

MAIN.CPP
#include “mbed.h”

#include <MQTTClientMbedOs.h>

#include "CellularContext.h"

#include "CellularInformation.h"

#include "CellularLog.h"


int main()

{
    mbed_trace_init();

    CellularInterface  *net = CellularInterface::get_default_instance();

    CellularDevice * dev = CellularDevice::get_default_instance();

    ATHandler * devat = dev->get_at_handler();

    dev->soft_power_on();

    devat->cmd_start("AT+QCFG=\"iotopmode\"");

    devat->cmd_stop_read_resp();

}

MBED_APP.JSON

"target_overrides": {

        "*": {

            "platform.memory-tracing-enabled": true,

            "platform.stdio-baud-rate"                  : 115200,

            "platform.stdio-convert-newlines"           : true,

            "platform.stdio-buffered-serial"            : true,

            "platform.stdio-flush-at-exit"              : true,

            "rtos.main-thread-stack-size"               : 5120,

            "events.shared-stacksize"                   : 2048,

            "events.shared-eventsize"                   : 2048,

            "mbed-trace.enable"                         : true

        },

        "DISCO_L475VG_IOT01A": {

            "target.network-default-interface-type"     : "CELLULAR",

            "ppp.ipv4-enabled": false,

            "ppp.ipv6-enabled": true,

            "lwip.ipv4-enabled": true,

            "lwip.ipv6-enabled": true,

            "lwip.ethernet-enabled": false,

            "lwip.ppp-enabled": false,

            "lwip.tcp-enabled": true,

            "nsapi.default-cellular-apn": "\"\"",

            "nsapi.default-cellular-username": "\"\"",

            "nsapi.default-cellular-password": "\"\"",

            "cellular.debug-at": true,

            "QUECTEL_BG96.provide-default": true,

            "QUECTEL_BG96.tx": "D1",

            "QUECTEL_BG96.rx": "D0",

            "QUECTEL_BG96.pwr": "A5",

            "QUECTEL_BG96.rst": "A4",

            "QUECTEL_BG96.polarity": 1

        }

    },