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.