Hi Von, welcome to the forum!! Soft places in the floor usually means that water has been there. Owner's manuals are pretty generic and I am pretty sure wouldn't cover something like replacing part of a floor. Replacing flooring can be a pretty big job and I wish you luck with that. And if the floor has been wet, you have to wonder where the water came from. If it came from the roof or a wall, you would need to find the leak and repair it or you will be replacing the floor twice.
Several years ago I bought a pretty good book about RV maintenance and repair. It is titled "Trailer Life's RV Repair and Maintenance Manual." I found that Amazon sells it now, but the price is ridiculous. It might be out of print and they can charge a huge price. I know I didn't pay over $25 for it several years ago. Amazon's link to it is:
RV Repair and Maintenance Manual (RV Repair & Maintenance Manual): Bob Livingston: 0074470034957: Amazon.com: Books
You might also try to Google search it and see if you can find a cheaper copy.
The book was published in 2002 and is getting a bit outdated. It does cover slides so maybe some of it might be useful to you if you can find a copy.