You can unhide a collection by doing the following:

  1. Navigate to your Rapid Search Admin, Settings, Advanced menu.
  2. Scroll down to the "Hide resources" section.
3. Click on the "Hide collections" option, remove the selection from the collections you want to unhide and click on the "Select categories" button 

You are ready. Only the selected collections will be hidden and the deselected ones will be shown.

Relevant support articles: