If the little speaker spring is not there you need to find and install it- it is a tricky little thing and will easily disappear. Trust me.

If you need to clean up the back of the case and cover and search fruitlessly for a replacement gasket you will have to go to the next guide for checking the module and fixing common issues.

Re assemble the back cover. You can just pop it back on and make sure it seats properly. If all you need to do was install a new battery to get it working congrats you are done!