After saving my a file in vim, is there a way it can auto change tabs to white s . . .

Amandeep Singh:
After saving my a file in vim, is there a way it can auto change tabs to white spaces? I tried setting expandtab, shiftwidth, and tabstop in vimrc but no success.

My use case: While editing files using vim, I would like to use tabs rather than spaces.

OE:
Set expandtab and then run:

:retab