1. Login in to your MainWP Dashboard
2. Go to the MainWP > Extensions > Custom Post Types page
3. In the Custom Post Types box, you will be able to see all registered CPTs on your MainWP Dashboard
4. Locate the one you want to publish to your Child Site(s)
5. Click the Add New button
6. You will be prompted to the Add New screen
7. Enter the CPT post Title, Body, and metadata
8. Select your Child Sites where you want to publish
9. Click the Publish button

Please note that the Classic Editor plugin must be installed on MainWP Dashboard and related Child sites.