By default, MainWP Dashboard is designed to check for possibly abandoned plugins and themes once per day. But if you want to trigger this process manually:

1. Go to the MainWP > Sites > Manage page
2. Select Sites that you want to check
3. Select the Check Abandoned Plugins or Check Abandoned Themes action in the Bulk Actions menu
4. Click the Apply button.

The same process can be manually triggered from the MainWP > Updates page.

For Plugins, go to the MainWP > Updates > Abandoned Plugins and click the Check for Abandoned Plugins button.

For Themes, go to the MainWP > Updates > Abandoned Themes and click the Check for Abandoned Themes button.