Unhiding list SharePoint

1. Open SharePoint Designer
2. Click "all files" folder at the bottom of left pane
3. Right click on the hidden list from "all files" folder and choose property
4. Now hidden list is open in SPD
5. In list settings => Generally settings: Uncheck the "Hide from browser" and save.

Hiding List SharePoint

1. Browse the list 
2. Go to list settings
3. Go to general settings
4. Check the option "Hide from browser"
5. Uncheck option "Display the list on Quick launch"