While making sure the metal bar behind where the mainboard sits is down, fold the mainboard back ontop of it

Keep tight pressure on the main board near where the metal bar sits, and test to ensure that the trigger returns after pressing it in, otherwise, continue repeating attempting to put the mainboard back on until it does.

After confirming the trigger still functions, screw the mainboard back on, starting at the screws near the top.

Plug back in the black cable.