If you've signed up for the Miz Mooz email list before you enrolled in the Rewards program, you will receive an email from Miz Mooz with 'Miz Mooz Rewards Program' as the subject line containing the code you can enter at 'Ways To Earn Points' at https://mizmooz.ca/pages/loyalty-rewards.
In case you already received that email, search it in your box under 'Miz Mooz Reward Program'.