Mobile form – autosave or do we need a “Save” button? [closed]

When designing a mobile app that contains a forms with various fields what is the best approach:

1)autosaving and show return arrow to go back to previous screen

2)fill fields and show a save button

That form has also a submit button, that is disabled till all the mandatory fields are filled.

My guess is that the overall expectation of the user is to still see a "save" button.