Android Question How to press back button from app

I have a MAIN module that calls the EDIT module to add or update records.

This secuence works ok:
I call the EDIT with StartActtivity(EDIT)
In the EDIt, if I press the back button to cancel, then I return to the MAIN and if I press back button again I exit the app.

This does not:
In the EDIT, I have buttons for add edit or delete, when I finish the code the I go back to the MAIN with StartActivity(MAIN)
NOw if I press back button in the MAIN i go back to the EDIT module.

I suppouse it can be fixed by pressing the back button intead of the startactivity.

How can I press the back button from my app? or are there any other way?

Thanks