How do you convert an older electric range to a 4 wire plug when there is no bonding strap on the range It now has a 3 wire cord I need to convert it to a 4 wire cord.?

The difference between a 4-wire and a 3-wire is a separate ground and neutral. That being said, all you have to do is connect the ground wire to chassis ground, and the neutral wire directly to the neutral connection. The phase wires are made up the same as the old cord. You must also remove the bonding jumper, but if there isn't one... IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS. If you do this work yourself, always turn off the power at the breaker box/fuse panel BEFORE you attempt to do any work AND always use an electrician's test meter having metal-tipped probes (not a simple proximity voltage indicator) to insure the circuit is, in fact, de-energized.