What should I do if wrongfully approved a manuscript while references were incorrect?
Email the journal. This is something the publisher should be able to easily solve, since it's simply returning the paper to the author. Worst case scenario, the publisher can return a 'revise' decision and let you fix the problem.

It sounds like you've already done this and didn't receive a response for four days. This isn't particularly long - for example, perhaps the desk editor is on short-term leave and Springer didn't assign someone to cover. I would wait a bit. If you're in a rush you can also email the editor-in-chief; however, you write that the status is "pending editor assignment", which could mean that the editor-in-chief has not seen the paper yet.