Soft spot on the roof needs to be fixed need advice

Thanks everyone for the great responses. From what rjxj says it sounds like my assumption of pretty straight forward is about right.

B.O. I sure hope you are correct and it is not vacuum bonded. It that's the case then the inside bit of water damage should be easier to fix too but another time for that. Looks like I have a project to do in the next number of weeks. Will wait for a nice dry weekend to do this.