Connection to gas range gas line too large for gas line intake valve. How can I step the range back line down a step. Is there some kind of converter I can buy? [for the gas intake valve]

Assuming you have a 3/4" piping and a 1/2" valve. You can reduce pipe size by using a 3/4 to 1/2" reducing coupling , or remove last piece of 3/4" pipe , install a 3/4 to 1/2 bushing in the fitting and re-pipe with 1/2" pipe. Use black pipe, not galvanized and pipe thread compound. Check for leaks with Mr Bubbles. Double check for leaks.

Thank you. I am sending someone to get the part and materials right away.