How do I get the Windows 10 preview key?

[Windows Central Question]

how do i get windows 10 preview key

i am a windows 10 preview insider tester and i got the second to last update just fine but when i went to install the final build my laptop locked up so i reverted back to the second to the last build. now i wish to do a fresh install and it keep asking me for a key. is there a way to retrieve this from microsoft