[Q] Could not do normal boot- how to fix what I don't know was done topic

I got a phone from a relative who is not clear on what he did- but I think he likely rooted his S4, then accepted an update. I'm a full time IOS guy with some Android/Samsung experience, but I don't know where to start. If all I can get is "could not do normal boot...downloading do not turn off target" on this Verizon Samsung S4- where the heck do I start? I'm familiar with what ODIN is - but I'd need a version number and files to upload right?:)
Thanks in advance.