"Dewa" for changing the subject


If someone is speaking about a subject that you're not comfortable with can
you say "dewa" to change topic?




No. では (or それでは) is like "Okay then, ..." which is primarily used to
_continue_ the current topic based on what was said. では is also used to return
to the main issue after digressing, like "Okay now, (let's start ...)".

If you want to switch to a totally new topic, you should use ところで (≒"by the
way"), それより (≒"before that"), etc.

