some time ago i was asked to "revive" a washed 4th gen. nano
i was not able to save it - cooked/dried and came to me after 2 month....
first of all - if it was wet - it will die - you can only try to change the "time of death"
disassemble it as described in the 5th gen. teardown
clean it with IPA - i prefer special cleaning solutions for pcb's - but not everybody has them around and it should be easier to get rubbing alcohol
use a paintbrush to clean it
maybe you should take a look at this page: [http://www.blue-backlight.de/de/umbau_de/umb_Wasserschaden.htm|CLICK]
use google (or what ever you prefer) to translate it
good luck