CASE formula for switching text within a field

I'm trying to put a CASE filter on a field and keep getting errors.

My goal: When the text in the field contains a comma, change it to a semi-colon.

I believe I'm getting hung up on what verbiage to use (contains?) in the case statement.  Ultimately, I need to export csv data from a report and whenever a comma is in the field, it errors out.

Here's what I have currently: CASE Campaign."Campaign Name" WHEN ',' THEN ';' ELSE Campaign."Campaign Name" END

Regards