| No need for a diagram, the three wire dry cord should be flat, the center wire is the neutral, the two outer wires are the hots. Inside the dryer at the terminal strip, the center terminmal is neutral, the two outer wires are the hots.
The important item changing a 4 wire cord toa three wire on a dryer or range, is the center terminal must also have a wire jumper from the neutral center terminal to to metal frame of the appliance. Sometimes there may be a metal strap given for this. In any case this must be done to ground the frame of the appliance.
Note, this is ONLY done with a 3 wire cord.
However, you can check to see if there may be a diagram pasted on the outside or even the inside of the backplate of the appliance | 
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