Verify connectors are correctly aligned then press down.

Gripping the GHA-472 board on the short sides with thumb and forefinger, gently press down to reseat the GHA-472 board onto the pin connectors on the PRCB-472 board
Use the forefinger to gently push down on the GHA-472 board. Do this at two or more points without damaging any of the board circuits or components.