Pixhawk 4 Mini: How do I enter ESC Calibration mode?

Hello together,

first of all, I am a total newbie to building and flying drones.

What I use:
Holybro 250 QAV Basic Kit with Pixhawk 4 Mini
Mission Planner 1.3.74
ArduCopter V4.0.7

I succesfully completed frame type and RC configuration, also accel and compass calibration, all according to the documentation. After compass calibration I am now somehow lost. I clicked reboot and afterwards connect in the upper right corner.

Next step is, as far as I can see, ESC calibration. So I disconnected pixhawk from my pc and powered it with the battery, RC throttle at maximum. But the flight controller does not enter ESC Calibration mode. The LED on the GPS just blinks yellow, not circulating through the colors as in the doc.

What am I missing? I would be very glad, if someone could help me out. Thanks in advance