White wire when changing from 4 prong to 3 on dryer

I recently moved into a home with a 3 prong outlet for my 4 prong Kenmore dryer. I went to Home Depot to replace the 4 prong plug with a 3 to match the outlet. I was ready to install the new plug when I noticed this white wire (2nd picture) and I'm not sure where it should be connected to. Originally on the 4 prong plug this white wire was connected to the middle screw (1st picture) but from the videos I've been able to see this seems to go to the ground (green screw). So my question is where should this white wire be connected to, the green screw or should I connect it once again to the middle bracket?

^{Original 4-wire cord}

^{New 3-wire cord}