How do I bring back missing thumbnails on my mobile device?

bring back missing thumbnails

Please do the following steps to bring those thumbnails back:
1. Touch the setting icon Inline image 1
2. Select Inline image 2, and scroll to the bottom of the setting page
3. Select delete thumbnails Inline image 3  
4. After that touch the setting icons Inline image 4
5. Select Library Inline image 5