Hmmm, well since Sophia has not had an opportunity to respond yet, I will offer up some thoughts along with caveats regarding credibility. I am a follower of this site, self taught (or at least Sophia taught) and find much of my focus is repairing children's books as a volunteer activity. I have 6+ years experience and much to learn. That said, consider looking for “skewed” or “slanted” spines.
Starting here, with course 2-205 addressing your topic. It is difficult to see from the attached photo if indeed the book is intact, meaning still in the case. If it is, the 2-205 course takes a fairly extensive approach that will involve some patience or previous repair skills. If you are NOT experienced with book repair and looking for a “quick fix”, YouTube might be a path to consider.
Another approach might be to consider topics in Reddit.
Generally speaking I personally would get the text block out of the case, clean off the spine to exposed signatures, then reline the spine with glue/material that will hold the text block in the position you want....perhaps with benefit of a press or large pile of books....for a while.