You could create a view of contacts using list membership as a filter (your import should have created a list) and use this to manually bulk set them as marketing contacts - this would most likely be easier than reimporting, would it work in your situation?
You could create a view of contacts using list membership as a filter (your import should have created a list) and use this to manually bulk set them as marketing contacts - this would most likely be easier than reimporting, would it work in your situation?