Power Apps Functions To Navigate between the screens:

Back() and Navigate() are the functions to navigate between the screens in the Canvas App.

Back() Function :
Back() function will be used for navigate from current screen to pervious screen .

Add The Back() function on OnSelect property of the controls like Button or icons.

Syntax:
Back()

Navigate() Function :
Navigate() function for move to specific screen in Canvas Apps.

Add The Navigate () function on OnSelect property of the controls like Button or icons.

Syntax:
Navigate(Screen Name )

Also you can use back function.But again it depends on your requirement.

1. Add a button or an Icon.
2. Select OnSelect function from the dropdown in the toolbar.
3. Navigate(ScreenToNavigate, ScreenTransition)