The Text Block can be found in the CMS here: https://app.contentful.com/spaces/eyc25wndlima/environments/staging/entries/1uq2mu0GlkiTY1mXsMRKs6?focusedField=cmsTitle
In the right hand side panel, you will be able to see the pages or content entries that are linking to this item.
You can also hover over the link count to the right of the Empty Placeholder Text Block [DEMO] title in the CMS to see all the linked pages
These pages will need their own Text Blocks or other Content blocks added to replace this one.