combining two rows wit the Query Builder

I have two rows showing up in mysql table
BC     taxyear     research     support     supervision
IOS    201704     $90000
IOS    201704                         $6234
I'd like to make these two lines into a single line like this
IOS     201704    $90000        $6234
I thought I could use group_by like this
$this->db->group_by(array("BC", "taxyear")); 
$this->db->insert('substantially_all_render_temp', $data);
But this doesn't work. What am I doing wrong? $data contains an array of the data I am placing into the table.

proof that an old dog can learn new tricks