I need to run a dedicated circuit for a new double convection oven. Its 240V, 40 Amp. The old oven that it will be replacing is on a 50 Amp breaker, & the wire gage appears to be #6, or even #4 aug. Is this wiring configuration compatible for the new oven, or do I need to run a new 8/3 home run?

I have moved your post, you posted it in the section to ask about your career, don't know why

Please watch where you are posting

Change the breaker to a 40 amp dbl. pole. Leave the larger wire in place, making sure the connections are done properly. You can oversize the wiring in a circuit, but you can't oversize the breaker.

Check for a neutral requirement. Usually it would say 240/120V.

Need to know the wattage or KW of the unit. If it draws 40 amps, or up to 9600 watts, then the 50 amp breaker needs to remain.