Does this help?
I used to do book repair for a library. This is the usual approved method for an in-tact text block that has separated completely from the cover. However, if you would like to take pictures of your damaged book, I can tell you what the method of repair should be.
The uninitiated will tell you to use common types of tape like duct tape, packaging tape, or school glue. Do NOT use those. They sell book binding tape and archival quality glue. Anything else will shorten the lifespan of your book, not lengthen it.