There are dozens of manufacturers who, combined, make hundreds of models of convection ovens. So…a #$%&*@ make and a model would sure be nice to know.
NOW, how do you confirm a centrifugal switch is bad? By using the oven’s schematic as a reference for determining WHERE in the circuit would be the easiest place to connect your multimeter. That would depend on the motor’s design too. On some ovens, the wiring is accessible on the motor. Others? Probably way up and behind the control panel.
There are various ways to test whether the centrifugal switch is working. You can use a voltmeter or an ohmmeter for doing that. Your choice.