The right hand medallion has two holes for a spanner type wrench. You will probably have to make a tool to avoid damage to the medallion. With the right grip off, the left can be removed from inside.
But be careful. The screws don't thread into the frame. The right hand medallion is a screw but it screws into a bar called the grip holder that locks into the frame. The left side is reversed, with a screw on the inside threading into the medallion through the grip holder on that side. So you don't need to unscrew the medallions all the way, just enough to let the bars loose from the frame.
Jim