You can continue to access the book if you have run out of time, so long as the publisher has not yet Archived it in NetGalley (which usually occurs on/after the pub date).
If you’re using the NetGalley Shelf app: Click here for renewal options within the NetGalley Shelf app.
If you’re using another supported device or app: Sign back into your NetGalley account, go to your Shelf, click the book title, and then press either the Send to Kindle or Download button.
More information about expiration and Archive dates is available here.