ios back button from a tab bar view controller

ios back button from a tab bar view controller

this is probably a very simple solution, i am writing an app for iphone
that helps people manage their medication for fibromalyosa (i spelt that
wrong i think....)
the first view controller of the app is a main menu (which is another
problem for another question about collection views)
the menu is embedded in a navigation view controller with the navigation
bar hidden to stop the menu looking squashed
the first item of the menu pushes a tab bar view controller with 3 tabs in
it (each tab has a view controller)
so here's my question:
how do i implement a back button on all 3 tabs that will send the user
back to the main menu?