A short distance away from the nails saw across the damaged
board. Place a strip of wood under the raised section of
board to support it. Lever the board at the other end and
remove all of it, or saw the other end of the section to
be replaced in a similar way. Attach softwood battens across
the joists to support the ends of the replacement section.
Check the width and depth of the new section is the same
as the rest of the floorboards. If the new section is not
as deep as the other boards it can still be used by packing
the end battens with plywood or hardboard before positioning
the new section.
If you need to cut across a board that lies close to a
wall, take care not to damage the bottom of the skirting
board. If you do not want to remove the skirting board,
drill a starting hole through the board along the side of
the joist. Use a power jigsaw or the blade of a pad saw
to cut across the board. Attach a softwood batten across
the joist to support the replacement board and continue
as above.