Unscrew the cutting arm cover and pull it out. (Bend the leg a bit to pull it out)
Repace the head into new one and connect the wire as it was to the head control board.
Wire sequence is sensor > head1 > head2 > head3 > head4.
Just for your info, the white flat cable goes to pressure control board (driving board).
Pressure control board’s wires for each head is going to main board as below.