CircuitPython
Setup
The Pro Micro - RP2350 is included in the latest release of CircuitPython. If you've never used CircuitPython before, take a read through their tutorial here or click the button below:
Thing Plus - RP2350 Firmware
Download the latest firmware for the Pro Micro - RP2350 from the CircuitPython downloads page and search for "Pro Micro RP2350".