If you're talking about the plate that is connected to the steering shaft, push down on the plate and you should be able to remove a wire retainer that holds the plate in place.
on earlier models a 7mm socket on the back plate works fine.
nevermind
You can find it under the dash board.
I also want to know that...
Were Under dssh is it
The turn signal flasher is under the the dashboard attached to a clip mounted to the steering column.
remove the glove box insert. a fuse panel is located there
In the fuse box under the dash on drivers side.
I have a 1990 Cutlass Calais. I had to remove a plastic panel under the steering Column. It was located to the left of the column under the dash.
Remove steering wheel (with wheel puller), remove lockplate (with lockplate remover), remove 3 screws that hold turn signal switch, unplug switch at bottom of column, fish out the wires, install new switch, fish in new wires.
Pull the turn signal lever towards you until it clicks, then let it go.
You have a bad turn signal flasher.
Very likely it's the turn signal switch.