Licenses for iShowU Instant are managed through Paddle, which is separate to the shinywhitebox store used for previous products.
To manage licenses for iShowU Instant you'll need to log in to your Paddle account at https://my.paddle.com/ using the email address you used when you purchased iShowU Instant. Once logged in you'll be able to see your iShowU Instant purchase and license code.
If you didn't set a password, then click the Forgot your password? link and you'll receive a password reset link from Paddle.
For more details about the difference between your shinywhitebox account and your Paddle account, see this article.