I'm trying to change the format of item list: Role, from text to list and the below message came up.
Do you know how can I fix it?
It means that line item is being used in a formula somewhere. Scroll to the right in blueprint and check to see what's using that line item. That formula will need to be changed before you can use this line item. But, the good news is that Role should be list formatted line item, so you're on the right track!