You can reset your password in the Settings page.
If you're using the app:
Tap the "Profile" icon (the green circle containing your initials) in the top right corner of your main offer page, then "Settings & Preferences" under "Info", towards the bottom of the page. Click the link that says “Reset password,” and follow the steps.
If you're using the website:
Log in to your account, then go here: http://www.checkout51.com/account/forgot