The plugin is similar to the Find unlinked children bulk post action, but allows children to be selectively linked.
To use the plugin, select one post in the post overview. If you select several posts only the first will be used.
Select the Find some unlinked children bulk action and wait for the popup to appear. The time taken depends on how many blogs are in the network. When the popup is fully loaded you will see a list of blogs that contain a post with the exact same slug as the post you have selected.
Chose what to do with each unlinked child and then press the button. The selected posts will be linked and the page will reload.