Mark off the area of buckled floorboards, using masking tape.
Set the depth of your circular saw to the depth of the replacement board. Stick the blade between the boards of your floor if you can fit the blade down between and extend the blade until it touches the subfloor beneath.
Turn on the saw and cut down the middle, lengthwise, of your damaged board. Cut the next board in a parallel line to the first cut.
Lift up the old board with a pry bar, grabbing the nails as you go. Hit the floorboard with a chisel and hammer if it is glued down or stuck in place.
Cut the lumber for the replacement board to the size of the hole in your floor. Press the board in place and nail the board down every 6 inches, using a hammer.