I have a list where I store groups that are required to fill up a form, and every group has his user list stored in a Person/Group field with multiple values enabled. What I want to do is a workflow that every time a user fill up a form, his name will be removed from this multiple value field based on a group ID. I already tried replacing his name with a blank space but it didn't work, any idea of how can I remove a name from a multiple person field?

Thanks.