Use a 3-pin JST-PH cable to connect the button to the sensor port on the HalloWing. Cut the cable so it's at least 76mm(3in) in length. The button only needs two wired connections so we can cutoff the red (middle) wire from the cable. Using wire stripper, remove a bit of insulation. To make it easier to attach the wire to the button, tin the exposed strands of wire with a bit of solder.
I suggest using a pair of third helping hands to hold the button in place while soldering. Solder the two wires to the pins on the button. The JST-PH connector from the cable plugs directly into the sense port on the HalloWing M0 Express.