How does a peanut like me get the propellor to stop spinning if it’s attached to a hot Lycoming or Continental in the air? I know from first-hand experience that it’s not by turning the fuel off or the magnetos off, or both.
Pull the mixture and hold in level stall till it stops ..... re-establish glide and use starter to get it turning again - when you're ready - or do a dive and see what speed autorotation commences. Over an airport may be prudent.