Unutilized H1B expiring in Sep. 24

The visa is unutilized and will not be extended as I haven’t been employed yet. I haven’t travelled. What can I do with this approved H1B after the stamp expires ?
What is the last date for extending the H1B period if I manage to travel before it expires ?

You can find a new H1B employer and transfer your H1B. Once approved you can go for visa stamping and travel to the US. There is no last date to reclaim any remainder of time left on your H1B 6 years term.