How to Filter the Multiple Values.

As of now Tableau does not have "IN" operator to use in the Calculation but there is an alternative that is "OR"

Case [Region]
when "Central" then "Territory - 1"
when "East" then "Territory - 1"
else "Territory - 2" end

Or

If  [Region] = "Central" or   [Region] ="East" then "Territory - 1"
else "Territory - 2" end