Accessing specific fields within advertising data

[Nick_RA]

My AD data is defined with macros as such:

static struct bt_data ad[] = {      BT_DATA_BYTES(BT_DATA_FLAGS,
                                    (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
                                    BT_DATA(BT_DATA_NAME_COMPLETE,
                                    DEVICE_NAME,
                                    DEVICE_NAME_LEN),
                                    BT_DATA(BT_DATA_MANUFACTURER_DATA, mfg_data, sizeof(mfg_data)),                                    
                                    };

I need to change the manufacturer data then update the advertising data using

bt_le_adv_update_data(ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));

My question is: How do I get a pointer to mfg_data - is there a helper macro for this?