WordPress says the zip file is invalid when I try to upload the plugin.
Please first unzip the file you downloaded from Code Canyon. There will be a second zip file inside called post-planner.zip that contains the actual plugin files.

How can I change who can read/add/edit/delete Planners?
If you want to prevent them from access Planners entirely, uncheck the user role from under Settings > Advanced > User Roles Allowed Access.

If you want to use an external role editor plugin to manage user access, set Settings > Advanced > Disable Default User Roles to Yes and configure your plugin of choice to set the Planner’s capabilities. The plugin’s capabilties end in _planner or _planners. Members or User Role Editor are two plugins that can do this.

Why is the checklist not showing up?
You need to set up the checklist items under Settings > Post Planner > Checklist Items.

How do I change the Status choices?
You can change the Status choices under Settings > Post Planner > Statuses. The first choice is the default choice.

How I export the Planners or Settings?
You can export the Settings from Settings > Post Planner > Import/Export.
You will need to use the default WordPress import/export feature under Tools to export the Post Planners.