Important Note:
This article relates to the legacy OptimizeMember. To find documentation for the new OptimizeMember (released 2022) please visit the new OptimizeMember documentation
OptimizePress currently do not have built-in options that could prevent users from accessing WordPress dashboard. As of now, the only way to prevent non-admin users from accessing WordPress dashboard is to use third party plugin. You can use this:
https://wordpress.org/plugins/remove-dashboard-access-for-non-admins/