First time programming still needs a hardware connection to be made between P1.5 and GND, but after that holding the 1st key while connecting USB lands you in the bootloader!
If your board is never used with ch55xduino before, you need to make the ch55x chip enter bootloader mode. You need to disconnect USB and unpower ch55x, connect the pull-up resistor on D+ line (generally a 10K resistor between D+ and 5V, controlled by a push-button or adjacent pads). Then you connect USB. and hit Upload. Also, a blank new chip will enter the bootloader automatically.
