Was this a paper LUV voucher or emailed LUV voucher or some other type of voucher?
If you lost it and its not expired you could try to reach out to Southwest on Facebook or Twitter and maybe they can help and possibly resend it. You could also reach out to customer relations at 855-234-4654 and they might be able to help.
In the fine print it says lost vouchers can’t be replaced but hopefully they can make an exception and help with resending the voucher or maybe they can void the the lost voucher and issue a new one.
-Blake
