Updating a staging site will copy the database and files from the live site to the staging site again. To do that,
- Login to your MainWP Dashboard
- Go to the MainWP > Extensions > Staging page
- Locate the wanted child site
- Click the Manage Staging Sites action (you will be redirected to the page where you can see your staging sites for the child site)
- Locate the staging site that you want to update
- Click the Update action link