Use alligator clip leads to connect the Plant Monitor to your Circuit Playground Express. Note that the choice of lead color is just to match up with the photo below.

• Black - GND on the Plant Monitor to GND on the Circuit Playground Express. I suggest the GND near the battery connector of the Circuit Playground Express
• Red - 3V on the Plant Monitor to 3.3V on the Circuit Playground Express
• Yellow - RX_IN of the Plant Monitor (downwards arrow) to the TX A7 ring of the Circuit Playground Express
• Green - TX_OUT of the Plant Monitor to the RX A6 ring of the Circuit Playground Express