How do you wire a 4 prong dryer cord to a 3 wire receptacle?

Using a red wire nut hook the 3 wires (of the same color) together with a short piece of wire of the same color. You now have 4 wires tied together.

Now take the other end of the short wire and attach it to the outlet on the correct screw

Do the same with the other 2 wires

Please keep in mind to make sure the wire nut has securely fastened the wires.

Loose connections cause heat which cause fire

If you do not completely understand this answer please contact a qualified electrician