You can upload to the core first this code (I'm using the Gray core):

#include <M5Stack.h>

HardwareSerial GPS(2);

void setup() {
GPS.begin(9600);
Serial.begin(115200);
}

void loop() {
for (;;) {
if (GPS.available() > 0)
Serial.write(GPS.read());
if (Serial.available() > 0)
GPS.write(Serial.read());
}
}

In u-center set the baud rate to 115200. Go to View-Messages View (F9), expand UBX-CFG-MSG and check UART1.

In my case the satellites detection only works outdoors.